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  • 1995-1999  (1,117)
  • 1997  (1,117)
  • Theoretical, Physical and Computational Chemistry  (699)
  • Chemical Engineering  (418)
  • Nuclear reactions
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  • 1995-1999  (1,117)
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Keywords
  • 1
    Electronic Resource
    Electronic Resource
    Vapor-liquid equilibria of the ternary mixture CH4 + C2H6 + CO2 from molecular simulation (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 212-217 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The NpT + test-particle method for the calculation of vapor-liquid equilibria by molecular simulations is extended to ternary mixtures. It is applied to the system methane + ethane + carbon dioxide, for which all binary molecular interaction models are available from previous work. Methane is described as one-center Lennard-Jones fluid, ethane as two-center Lennard-Jones fluid, and carbon dioxide as two-center Lennard-Jones plus point quadrupole fluid. The unlike interactions are treated in the same way as the binary mixtures, using two parameters for each binary interaction. No ternary parameters are introduced. Vapor-liquid phase equilibria are calculated for the ternary mixture at the following temperature-pressure pairs: 233.15 K - 2 MPa; 250.5 K - 2 MPa; and 250.5 K - 3.04 MPa. Comparison of the simulation data with experimental and equation-of-state results shows excellent agreement. Bubble and dew densities are also reported.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430123
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  • 2
    Electronic Resource
    Electronic Resource
    Recovery and purification of paclitaxel using low-pressure liquid chromatography (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 232-242 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An efficient and economical low-pressure liquid chromatography process has been developed for paclitaxel recovery and purification directly from plant-tissue culture (PTC) broth. PTC broth is first diluted with ethanol to ensure padlitaxel dissolution and then passed through a column packed with a high-capacity polystyrene divinyl-benzene sorbent. A step increase in ethanol concentration in the mobile phase (ethanol:water) is used to concentrate and compress the taxane bands to as high as 29-fold of influent concentrations (about 1 mg/L). A recycle technique is then used to separate the concentrated paclitaxel band from other taxane bands, achieving 95% purity with more than 90% recovery and 99% purity with more than 80% recovery. In this process, the same low-pressure columns are used to capture, concentrate and purify paclitaxel. Theoretical predictions agree closely with the stepwise elution and recycle chromatography data. After validation, simulations are used to explore various design and operating alternatives. Analysis of the alternatives shows that the process cost can be further reduced by using higher feed concentration, larger loading volume, smaller particle size, and optimal gradient and recycle strategies.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430125
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  • 3
    Electronic Resource
    Electronic Resource
    Intensity of segregation revisited (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 263-264 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430129
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  • 4
    Electronic Resource
    Electronic Resource
    Analysis of nucleation and crystal growth data using the interfacial supersaturation (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 268-272 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430131
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  • 5
    Electronic Resource
    Electronic Resource
    Letters to the editor (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 281-282 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430134
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  • 6
    Electronic Resource
    Electronic Resource
    Boiling heat transfer of Nitrogen in a thermosyphon condenser-reboiler (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 339-344 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An experimental investigation was conducted to determine the boiling heat-transfer characteristics in a thermosyphon condenser-reboiler of air-separation plants. The test section was a plate-fin heat exchanger of practical size of 0.106 m width and 2.56 m length. The testing fluid was nitrogen. Experiments were carried out within a range of pressure from 150 to 300 kPa, submergence from 1.95 to 2.80 m, and heat flux up to 11 kW/m2 under constant wall-temperature condition. The liquid superheat at the onset of boiling was rather significant. The boiling heat-transfer coefficients obtained agreed well with Chen's correlation modified by Colburn's J factor within a mean deviation of 9.3%.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430207
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  • 7
    Electronic Resource
    Electronic Resource
    Comminution of limestone during batch fluidized-bed calcination and sulfation (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 363-373 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Batchwise fluidized-bed calcination and sulfation of a limestone were done to investigate particle comminution phenomena and their relation with parallel occurrence of reactions. Operating conditions of the bed were those typical of atmospheric bubbling fluidized-bed combustors. A general framework of comminution phenomena is outlined, which includes different types of fragmentations as well as attrition by abrasion. Comminution processes were characterized by following the modifications of bed sorbent particle-size distribution and the elutriation rates of fines throughout conversion. Mutual interactions between comminution processes and the progress of chemical reactions are assessed.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430210
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  • 8
    Electronic Resource
    Electronic Resource
    Vacuum membrane distillation: Experiments and modeling (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 398-408 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Vacuum membrane distillation is a membrane-based separation process considered here to remove volatile organic compounds from aqueous streams. Microporous hydrophobic membranes are used to separate the aqueous stream from a gas phase kept under vacuum. The evaporation of the liquid stream takes place on one side of the membrane, and mass transfer occurs through the vapor phase inside the membrane. The role of operative conditions on the process performance is widely investigated in the case of dilute binary aqueous mixtures containing acetone, ethanol, isopropanol, ethylacetate, methylacetate, or methylterbutyl ether. Temperature, composition, flow rate of the liquid feed, and pressure downstream the membrane are the main operative variables. Among these, the vacuum-side pressure is the major design factor since it greatly affects the separation efficiency. A mathematical model description of the process is developed, and the results are compared with the experiments. The model is finally used to predict the best operative conditions in which the process can work for the case of benzene removal from waste waters.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430213
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  • 9
    Electronic Resource
    Electronic Resource
    Application of a control-law nonlinearity measure to the chemical reactor analysis (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 425-439 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The optimal control structure has been introduced as a design tool to measure the control-law nonlinearity of a given process design. In this context, control-law nonlinearity is the optimal degree of nonlinear compensation in the controller, a system property distinct from open-loop nonlinearity and determined by a performance objective and the region of operation as well as the nature of the open-loop system. This approach is extended to the analysis of multivariable systems with output feedback through the application of an extended Kalman filter. Coherence estimation is used as a practical method to measure continuous, open-loop multivariable system nonlinearity. The CSTR with van de Vusse kinetics, a system that features output feedback and a controllaw nonlinearity that changes with operating points, is analyzed. The optimal control structure approach with coherence estimation correctly indicates changes in the controllaw linearity between different operating points and changes as the regions of operation change around a particular operating point.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430216
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  • 10
    Electronic Resource
    Electronic Resource
    Rate parameters and gradient correlations for gradient-elution chromatography (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 464-474 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Rate parameters and gradient correlations of proteins are very important to engineering investigations of gradient-elution chromatography. Before carrying out computer simulations for gradient process, these rate parameters and gradient correlations must be determined from experimental data. This work presents a systematic method for estimating and determining these parameters and correlations using experimental data and computer-simulation results based on isocratic runs. The values determined were then employed in gradient-elution studies by putting them into the rate model to perform computer simulations. Experimental runs under gradient conditions using the parameters and correlations just referred to were carried out in a DEAE Sepharose CL-6B ion-exchange chromatography. Comparisons between the experimental data and the simulation results show good agreement.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430219
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  • 11
    Electronic Resource
    Electronic Resource
    Granulation of sol-gel-derived nanostructured alumina (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 505-514 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A sol-gel granulation process was developed to prepare porous nanostructured γ-alumina granules as supports for catalysts and adsorbents. The process, which starts with an aqueous sol of gelatinous boehmite, involves droplet formation, gelation in paraffin oil, conditioning in ammonia solution, and drying and calcination in air under controlled conditions. The γ-Al2O3 granules prepared are 1-3 mm-dia. spherical particles with large surface area (380 m2/g) and pore volume (0.5 cm3/g), uniform pore-size distribution (20-60 Å), and controllable average pore size (35 Å). These sol-gelderived granules have excellent mechanical properties with crush strength (〉100 N per granule) and attrition resistance (〈0.01 wt. %/h), much better than the commercial alumina and zeolite granules. Supported CuO sorbents were prepared on these granules for SO2 removal applications. The alumina-supported CuO sorbents contain higher loading of well-dispersed CuO and better sulfation properties than similar sorbents reported in the literature.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430223
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  • 12
    Electronic Resource
    Electronic Resource
    Molecular thermodynamics of heat-induced protein unfolding in aqueous media (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 525-534 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The molecular thermodynamic model studied is based on the two-state mechanism of inactivation, in which only native folded and polymorphous unfolded protein forms are present at equilibrium. The influence of solvent on protein stability is described in terms of perturbation of the protein distribution between the two conformational states. An expression derived for the chemical potential of the protein accounts for conformational changes, ideal mixing effects, and interaction of the protein with the surrounding medium.Thermal unfolding of lysozyme was then studied in the absence or presence of hydroxylic compounds. Ultraviolet difference spectroscopy was used to monitor the conformational changes induced by heating and to determine the melting temperature of the protein. The additives investigated are ethanol, glycols, and natural osmolytes. Media containing ethanol and glycols destabilized lysozyme, whereas sugars increased the conformational stability of the protein. For all of the systems examined the melting temperature was linearly related to the surface tension of the mixed solvent, supporting the ability of the model to describe the influence of the solvent and composition on lysozyme unfolding. Model predictions agreed fairly well with published differential scanning calorimetric data. The influence of hydroxylic additives on protein's conformational stability does not extend to any special property of these components, but to their ability to perturb the surface tension of water. This model can be used to interpret and correlate thermal unfolding data and to solve the problem of protein stabilization.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430225
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  • 13
    Electronic Resource
    Electronic Resource
    Masthead (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997) 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430301
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  • 14
    Electronic Resource
    Electronic Resource
    Colloidally induced smectitic fines migration: Existence of microquakes (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 565-576 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The phenomenon of colloidally induced fines migration is a challenge of both scientific and industrial importance. Its occurrence impacts permeability reduction and alteration of flow pathways in porous media, particulate contaminant migration in groundwater flow, and filtration. The release of smectitic fines is a threshold type of process resulting from discontinuous jumps, called microquakes in the interlayer spacing. There is a critical salt concentration at which these microquakes occur and produce fines migration in the porous media. The changes in the microstructure with decreasing salt concentration were analyzed using X-ray diffraction. The transition between crystalline and osmotic swelling regime is also shown to depend on the type of cation. A mathematical model developed using colloidal principles predicts the swelling behavior of smectites in aqueous solutions. The model can predict the transition of swelling from crystalline to osmotic regimes and explain the effect of different cations on the transition.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430302
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  • 15
    Electronic Resource
    Electronic Resource
    Unsteady heat and mass transfer from a spheroid (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 609-614 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The unsteady heat-transfer processes from oblate or prolate spheroids, at the limit of very small Peclet numbers is examined. A perturbation technique for the temperature and the geometry of the particle is used to obtain the rates of heat and mass transfer, first in the Laplace and then in the time domain. A solution to the problem is obtained, including the ∊2 contribution (∊ is the eccentricity). The solution reveals the existence of several history terms, which are analogous to the history terms of the creeping flow equation of motion. One of these terms is solely due to the eccentricity of the spheroid. This is an indication that the shape of the particle is a factor of the existence and from of history terms. In addition, an exact expression for the steady-state heat transfer from a spheroid is obtained using a convenient transformation of the heat-transfer integral.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430306
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  • 16
    Electronic Resource
    Electronic Resource
    Perturbation solution to the convection-diffusion equation with moving fronts (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 631-644 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Electrophoresis of a solute through a column in which its transport is governed by the convection - diffusion equation is described. Approximate solutions to the convection - diffusion equation in the limit of small diffusion are developed using perturbation methods. The diffusion coefficient and velocity are assumed to be functions of space and time such that both undergo a sudden change from one constant value to another within a thin transition zone that itself translates with a constant velocity. Two cases are considered: (1) the thickness ∊f of the transition zone is negligible compared to the diffusional length scale, so the zone may be treated as a singular boundary across which the diffusion constant and velocity suffer discontinuous changes; (2) the transition zone is considerably wider than the diffusional length scale, so the diffusion coefficient and velocity, although sharply varying, are smooth functions of position and time. A systematic perturbation expansion of the concentration distribution is presented for case 1 in terms of the small parameter ∊ = 1/Pe. A lowest order approximation is given for case 2. A suitably configured system analyzed here can lead to progressive accumulation, or focusing, of the transported solute. The degree of focusing in case 1 scales with ∊-1, whereas in case 2 it scales with (∊f∊)-1/2, and thus increases much more weakly with increasing Pe. A separation based on this concept requires development of materials and devices that allow dynamic tuning of the mass-transport properties of a medium. This would make it possible to achieve progressive focusing and separation of solutes, such as proteins and DNA fragments, in electrophoretic media with an unprecedented degree of control.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430309
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  • 17
    Electronic Resource
    Electronic Resource
    Solid-phase creep during the expression of palm-oil filter cakes (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 665-672 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: For an adequate model of the processes of compressible cake filtration and mechanical expression, permeability and compressibility data are required. Experimental and modeling results of the creep behavior of palm-oil filter cakes at constant and time-dependent pressures are presented. Creep curves of palm-oil filter cakes at constant pressures cannot be modeled with linear viscoelastic models. Modeling with a modified form of the empirical equation of Nutting gives satisfactory results. This modification does not lead to unrealistic values of the porosity at extreme conditions, contrary to the original form of the equation of Nutting. Creep curves at time-dependent pressures were modeled with two nonlinear viscoelastic models, which describe the time-dependent creep behavior as a function of the pressure history and creep curves at constant pressures. Modeling with the strain-hardening model provides the best porosity predictions.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430312
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  • 18
    Electronic Resource
    Electronic Resource
    Effluent concentration profiles in centrifugal partition chromatography (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 693-702 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Centrifugal partition chromatography (CPC) is a relatively new preparative chromatographic technique. To understand, predict, and optimize CPC separations a model is needed, describing the effluent concentration profile as a function of the phenomena that determine the separation efficiency (mass transfer, mixing, and partitioning). The model presented in this article describes experimental effluent concentration profiles accurately. Partition coefficients, Stanton numbers, and Péclet numbers were obtained by comparing model simulations to experimental pulse-response data. The fitted partition coefficients agree well with those obtained from shake-flask experiments. Mass-transfer limitation is the major reason for peak broadening. The inverse mass-transfer coefficient is a linear function of the partition coefficient. The model will be a valuable tool in determining the influence of mass transfer as a function of various experimental conditions.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430315
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  • 19
    Electronic Resource
    Electronic Resource
    Identification of full profile disturbance models for sheet forming processes (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 727-739 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In this article we present a method for the on-line identification and modeling of full profile disturbance models for sheet forming processes. A particular principal components analysis technique called the Karhunen-Loève expansion is used to adaptively identify the significant features of the profile. In addition, we show how the temporal modes of the reconstructed profile can be modeled using low-order linear autoregressive (AR) processes. By simulation examples, the effect of the order of the AR model is studied, as well as the window size of the data used in the on-line application of the KL expansion, the effect of data weighting, the importance of the correct selection of the number of modes, and the frequency of updating the parameters of the AR models. Identified disturbance models can be easily incorporated into model-predictive control algorithms.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430318
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  • 20
    Electronic Resource
    Electronic Resource
    Kinetics of hydrocarbon adsorption on activated carbon and silica gel (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 761-776 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experimental breakthrough results of methane, ethane and propane in activated carbon and silica gel obtained over a wide range of gas compositions, bed pressures, interstitial velocities, and column temperatures were analyzed using a dynamic, nonisothermal, nontrace column breakthrough model. A linear driving force (LDF) approximation is used for particle uptake, and the Langmuir-Freundlich isotherm represents adsorption equilibrium. The LDF mass-transfer-rate coefficient (and, hence, effective particle diffusivity) and column-wall heat-transfer coefficient were determined. The results show that hydrocarbon transport in the activated carbon particles used is essentially by Knudsen and surface flow, while for the silica gel used the transport is primarily by Knudsen flow. For activated carbon, the experimentally derived LDF coefficients for all three sorbates are well correlated using an average effective diffusivity value. With regard to heat transfer, the column-wall Nusselt number is approximately constant for the range of Reynolds numbers considered. Simulations of multicomponent breakthrough in the activated-carbon bed based on independently measured single-component kinetic parameters and the extended Langmuir-Freundlich isotherm agree very well with experimental results. The computational efficiency gained by adopting the simpler extended Langmuir isotherm model is also investigated.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430321
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  • 21
    Electronic Resource
    Electronic Resource
    Two-flux radiation-field model for an annular packed-bed photocatalytic oxidation reactor (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 792-801 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: One of the remaining challenges in application of heterogeneous photocatalysis for treatment of air streams containing dilute VOCs is to design a cost-effective photocatalytic reactor that simultaneously allows efficient contact of the contaminated air and solid catalyst while uniformly irradiating the solid catalyst with light. A pseudohomogeneous model was developed to study effects of system parameters on process performance for a gas-solid lamp-in-tube annular-photocatalytic-oxidation (PCO) reactor in which the annular space is filled with photocatalyst-coated packing. In this model the flow field is assumed to be uniform and radial diffusion negligible. Homogeneous reactions are neglected. Heterogeneous reaction rates follow Langmuir-Hinshelwood-Houghen-Watson kinetics with rate parameters extracted from independent experiments. A 1:D “two-flux” incidence submodel is used to account for the radial UV light distribution throughout the reactor annular space. This submodel requires knowledge of the UV lamp radiant emittance, the optical characterstics of the catalytic thin-film coating, and the UV irradiance at the outer wall of the reactor and contains only a single adjustable parameter - the mean free path between photon-catalyst interactions. The model was validated with experimental performance measurements for destruction of acetone and isopropyl alcohol in a bench-scale photoreactor. The validated model can be used to predict the optimum catalyst film thickness for given reactor dimensions, packing shape and size, and VOC abatement problem.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430324
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  • 22
    Electronic Resource
    Electronic Resource
    Current distributions governed by coupled concentration and potential fields (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 811-817 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Results from steady and unsteady, two-dimensional simulations of tertiary current distributions at and below the limiting current density are presented. The simulations are based on dilute-solution theory, with coupling of the concentrations of the ionic species through the electrical field. The electrical field is calculated from the electroneutrality constraint. Results confirm and extend previous theoretical predictions of the electricalmigration enhancement of the limiting current. To demonstrate the potential utility of general current-distribution solvers, measured temporal variations of the rate of copper deposition in the presence of an oscillating shear flow are measured and simulated. Experiments agree well with simulations.
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    URL: http://dx.doi.org/10.1002/aic.690430326
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    Darcy constant for multisized spheres with no arbitrary constant (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 835-836 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690430328
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    Centrifugal analysis of pivoted-rotor systems for capillary pressure measurements (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 837-843 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690430329
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    Macro- and microscopic fluid transport in living tissues: Application to solid tumors (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 818-834 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Transvascular and interstitial fluid movements are involved in many important biological processes such as convective macromolecular transport and contribute to the mechanical behavior of tissue. Although intimately coupled, there is a tendency in the literature to regard these two fluid-transport mechanisms separately; if the interaction is considered, the description is usually confined to the local level (e.g., transvascular or interstitial perivascular). A general framework presented here combines transvascular and interstitial fluid movement with the mechanics of soft tissue and integrates macro-and microscopic views of the phenomena. On the macroscopic level, interstitial fluid transport is described by adapting the field equations of the poroelastic theory using average field variables defined on a scale of several blood vessel diameters (∼ 1 mm), while transvascular transport is described by a generalized Starling's law. As an example, the model equations have been specialized for a spherical solid tumor and an analytical solution is presented for the transient redistribution of interstitial fluid following a rapid change in vascular pressure or flow. The model describes the overall average profiles of the interstitial fluid pressure and velocity, as well as the dilatation, displacement and stress of the solid matrix. Moreover, on a smaller length scale the model can describe the local fluid movement (perivascular) using the average field variables as boundary conditions. The basic theory provides new insight into understanding the fluid transport in biological tissues and a valuable tool for determining relevant fluid-transport parameters. Implications for improving drug delivery to solid tumors are also discussed.
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    URL: http://dx.doi.org/10.1002/aic.690430327
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    Sherwood number for a swarm of adsorbing spheroidal particles at any peclet number (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 844-846 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690430330
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    Solvatochromic study of basic cosolvents in supercritical ethane (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 847-850 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/aic.690430331
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    Masthead (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997) 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430401
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    Effects of particle-phase turbulence in gas-solid flows (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 853-869 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Numerous experimental investigations on the vertical transport of dense gas-solid suspensions indicate that particles tend to segregate toward the tube wall. Although models based on the kinetic theory analogy can predict such patterns for perfectly elastic particle-particle collisions, the predictive ability of these models breaks down for inelastic collisions. In the present effort, a mathematical model is developed that incorporates two mechanisms that give rise to the lateral segregation of solids: interactions associated with individual particles based on a kinetic theory treatment and interactions associated with collections of particles based on an analogy with single-phase turbulent flows. Although these two mechanisms have been treated independently by previous workers, their combined contributions to the overall flow behavior have not been thoroughly investigated. The effect of such a treatment on the sensitivity of the model predictions to the inelasticity of particle-particle collisions is explored. A key element in eliminating the undue sensitivity appears to be a consideration of the effects associated with the collective motion of particles on the kinetic theory expressions. The resulting model can predict the expected segregation patterns for systems characterized by inelastic collisions, as well as many of the other salient features of vertical gas-solid flows.
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    URL: http://dx.doi.org/10.1002/aic.690430402
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    Crystal unfolding and chain disentanglement during semicrystalline polymer dissolution (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 870-876 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Mathematical models developed describe the unfolding of polymeric crystals in the presence of a solvent followed by their subsequent disentanglement. A thermodynamic model considering the free energy changes during crystal unfolding was proposed to obtain an expression for the unfolding rate. A simplified version of this expression, assuming uniform crystal size, was incorporated into a continuum model to predict the dissolution kinetics of a semicrystalline polymer slab. The model yielded predictions of the crystalline and solvent volume fractions as a function of position within the slab, in addition to changes in the fraction of polymer dissolved as well as the degree of crystallinity of the polymer as a function of time. The degree of crystallinity of the polymer decreased with time and the plot of the fraction of the polymer dissolved as a function of time exhibited Case II behavior. The model predictions agreed will with experimental results obtained during dissolution of semicrystalline poly(vinyl alcohol) in water.
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    URL: http://dx.doi.org/10.1002/aic.690430403
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    Resonant microwave power absorption in slabs and cylinders (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 615-624 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Resonant power absorption is an important phenomenon during microwave heating. The resonances that occur when plane electromagnetic waves are incident on infinitely long cylinders and slabs are investigated as a function of sample dimensions. For cylinders two kinds of incident waves are studied: TMz when the electric field is oriented along the axis of the cylinder and TEz when the magnetic field is oriented along the axis. At a resonant condition the overage power absorbed by the sample is a local maximum. Due to attenuation within the sample the resonances decrease in intensity as the sample size increases. Using the dielectric properties of water, resonances are found to be a function of the ratio of the sample dimension to the wavelength of radiation, λs, in the sample. For slabs of thickness L and integer values of n, resonances occurred at L/λs = 0.5n; for cylinders of diameter D, resonances occurred at D/λs = 0.5n - 0.257. The generality of these relations to predict resonances in other food samples are shown using existing dielectric data. Resonances in cylinders for both polarizations occurred at similar radii. However, the radius at which the first resonance occurred for the TMz case was absent in the TEz case.
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    URL: http://dx.doi.org/10.1002/aic.690430307
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    Steady spontaneous capillary flow in partially coated tubes (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 645-654 
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    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A spontaneous, steady capillary flow is produced for a liquid index in a circular tube that is partially coated with a surface modifier to create a discontinuous wetting condition between upstream and downstream portions of the tube. As a means of demonstrating that the flow configuration may prove useful as a diagnostic tool in studies concerning capillarity and the physics associated with the moving contact line, average steady velocities are predicted and compared against a large experimental data set that includes the effects of tube dimensions and fluid properties. To access a wider range of tube diameters (0.516-9.88 mm), experiments are performed employing “U-tubes” tested in the low-gravity environment of a drop tower, in addition to straight capillary tubes tested horizontally in a laboratory. The sensitivity of the steady capillary flow to surface cleanliness is dramatic.
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    URL: http://dx.doi.org/10.1002/aic.690430310
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    Symmetric group approach to relativistic CI. I. General formalism (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 1-10 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: General formulas for matrix elements of spin-dependent operators in a basis of spin-adapted antisymmetrized products of orthonormal orbitals are derived. The resulting formalism may be applied to construction of the Hamiltonian matrices both for Pauli and for projected no-pair relativistic configuration interaction methods. From a formal point of view, it is a generalization of the symmetric group approach to the CI method for the case of spin-dependent Hamiltonians. © 1997 John Wiley & Sons, Inc.
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    Symmetric group approach to relativistic CI. II. Reduction of matrices in the spin space (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 11-20 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An algorithm for the evaluation of matrix representations of products of permutation operators and of one- and two-electron spin-dependent operators in a spin-adapted basis of the N-electron spin space is presented. In particular, the case of the basis functions in which p' electrons are described by products of singlet-coupled pairs is considered in detail. The N-electron spin integrals are, in this case, reduced explicitly to the (N - p') electron ones. © 1997 John Wiley & Sons, Inc.
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    Symmetric group approach to relativistic CI. III. Matrix elements for spin-dependent operators (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 21-34 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Matrix element formulas for spin-dependent operators in a basis of spin-adapted antisymmetrized products of orthonormal orbitals (configuration-state functions) are presented. The coefficients of one- and two-electron integrals depend only on the form of the spin-dependence of the operator and on the mutual arrangement of the orbitals which are singly occupied in the pertinent pair of the configuration-state functions. The formulas are useful in implementations of relativistic two-component CI approaches, such as the Pauli CI and projected no-pair CI method. They may be readily used within existing nonrelativistic SGA - CI codes. As examples of applications of the new formulae, spin-own-orbit and scalar spin - spin matrix elements were derived. © 1997 John Wiley & Sons, Inc.
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    Using full-CI algorithms in Bethe-Goldstone-type expansions of the correlation energy (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 35-43 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the early 1960s, Nesbet proposed to develop correlation energy in terms of two-, three-, four-, etc., electron contributions. This expansion was, in principle, applicable to a large number of electrons without a size-extensivity error. The now available full-CI algorithms may be used to obtain those expansions in terms of either occupied spin - orbitals or, more efficiently, in terms of sets of occupied or virtual molecular orbitals. Tests on the NH3 molecule with a DZP basis-set problem show the slow convergence of this approach. © 1997 John Wiley & Sons, Inc.
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    Unexpected CASSCF bistability phenomenon (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 45-54 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: One exhibits a problem in which two strongly nonorthogonal complete active-space self-consistent field (CASSCF) solutions are obtained. The problem concerns a molecular frame which presents two stable geometries at the CASSCF level, quinoidal and diradical forms, in disagreement with experiment which indicates a unique minimum corresponding to an intermediate geometry. Those two stable solutions are obtained in a significant domain of intermediate geometries and are related with the CASSCF wave functions of the two stable structures. Obtaining a reliable potential surface starting from CASSCF solutions (even from larger CAS) appears as a very difficult task. © 1997 John Wiley & Sons, Inc.
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    Traces of spin-adapted reduced density matrices (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 55-61 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The traces of the p-order reduced density matrices (p-RDM) split into independent contributions associated to the subsets of p-electron eigenstates of the Ŝ2 and Ŝz operators. Here, we report the partial traces for the blocks of the low-order RDMs corresponding to pure spin states of an N-electron system. A systematic method for calculating those of higher order RDMs is described and some useful relations are also given. All these relations which must be fulfilled independently by a RDM can be considered as N- and S-representability conditions © 1997 John Wiley & Sons, Inc.
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  • 39
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    Average energy of an N-electron system in a finite-dimensional and spin-adapted model space (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 63-65 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An expression for the average energy of an N-electron system in a finite-dimensional, antisymmetric, and spin-adapted model space (as, e.g., a full-configuration interaction space) is derived using elementary properties of the Hamiltonian in the Fock space. © 1997 John Wiley & Sons, Inc.
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    Nonempirical wave functions for very large molecules. II. The PRDDO/M/FCP method (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 67-76 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A variation of the frozen-core potential (FCP) method is developed and implemented within the modified version of the method of partial retention of diatomic differential overlap (PRDDO/M). The explicit treatment of core electrons is replaced with a potential based on the actual core-valence integrals rather than upon an arbitrary model potential. The core-valence orthogonality requirement is replaced by an energy shift operator. PRDDO/M/FCP calculations exhibit good agreement with ab initio calculations with the same basis set, while reducing the computational cost significantly. © 1997 John Wiley & Sons, Inc.
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    Maximum-entropy analysis of momentum densities in diatomic molecules (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 77-83 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The one-particle density in momentum space γ(p) is studied for diatomic molecules by using the maximum-entropy technique. The knowledge of one or more momentum expectation values 〈pn〉 provides approximations on the density γ(p) for any value of the momentum, which are convergent when increasing the number of known moments. Other unknown expectation values are estimated in terms of the constructed maximum-entropy densities. A numerical study of the quality of the approximations is carried out by means of experimental and theoretical data for the momentum expectation values involved. Experimental errors are also taken into account to have an idea of the sensibility of the results to the information from which they are obtained. © 1997 John Wiley & Sons, Inc.
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    Electron affinities of metals computed by density functional theory and ab initio methods (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 93-100 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An extensive computational study of the meal electron affinity was performed using the ab initio and density functional theory (DFT) methods. HF, MP2, MP3, MP4, QCISD, and QCISD(T) was used as computational methods, while the hybrid, local, and nonlocal DFT methods with the LYP, P86, PW91, and VWN correlation functionals were used. Two basis sets, one small and applicable to almost all metals (LanL2DZ) and one large [6-311 + + G(3df, 3 pd)] used only for small metals, were employed. The computed results were compared with the experimental data and the capabilities of the DFT methods to perform this study were discussed. © 1997 John Wiley & Sons, Inc.
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    The relative performance of the local density approximation and gradient-corrected density functional theory for computing metal-ligand distances in Werner-type and organometallic complexes (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 85-91 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optimized metal-ligand (M-L) bond lengths for 17 classical Werner-type transition-metal complexes were calculated using the local density approximation (LDA) and a gradient-corrected (GC) extension. GCs lengthen the bonds by between 0.02 and 0.09 Å relative to the LDA results. The latter range from 0.02 Å shorter than observed to 0.05 Å longer, while the GC data range from exact agreement with experiment to some 0.12 Å too long. The LDA rms deviation is 0.025 Å compared to the GC error of 0.070 Å. In contrast, data from the literature for organometallic species show that the LDA gives systematically too short M-L distances and GCs lead to a better agreement with experiment. The relative performance of LDA and GC functionals reflects the qualitatively different chemistries of organometallic and Werner-type complexes. The magnitude of the GC bond-length expansion for the latter correlates with the ionicity of the M-L interaction. © 1997 John Wiley & Sons, Inc.
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    CFPHGLF calculation of 3S excited states for heliumlike three-body systems (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 101-105 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The correlation-function potential-harmonic and generalized Laguerre function method (CFPHGLF) proposed recently by us is used to directly solve the Schrödinger equations of low-lying triplet states n3S (n = 2-5) for a set of heliumlike systems, including He, Li+, and Be2+. The eigenenergies converge fast and steadily with potential harmonics (PH) and generalized Laguerre functions (GLF). With 10 PH, the percentage errors in the convergent ionization energies for 23S, 33S, 43S, and 53S states of the helium atom are 0.548, 0.291, 0.247, and 0.265% relative to the Hylleraas CI variational values. Somewhat better precision is achieved for Li+ and Be2+ systems. © 1997 John Wiley & Sons, Inc.
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    Theoretical studies on the structures and electronic spectra of C70CH2 (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 815-822 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intermediate neglect of differential overlap (INDO) calculations were used to study the structure of C70CH2. It was found that the CH2 group is mainly added to the CI(SINGLE BOND)CII (CI represents the first kind of carbon atom and so on) or the CIII(SINGLE BOND)CIII bond in C70 and a cyclopropane feature with Cs symmetry is formed in the structure, which is in agreement with Smith et al.'s experiment. The electronic spectra of eight isomers of C70CH2 were calculated based on the optimized geometries. It was shown that the UV/vis spectra of C70CH2 and C70 resemble each other in many ways with the exception of the absorptions beyond 500 nm. The red-shift of the absorptions and NMR spectra of C70CH2 are discussed. © 1997 John Wiley & Sons, Inc.
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    Peptide models. XIV. Ab initio study on the role of side-chain backbone interaction stabilizing the building unit of right- and left-handed helices in peptides and proteins (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 797-814 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Previous ab initio computations revealed that the conformational building unit of the right-handed helix (φ ≈ -54°, ψ ≈ -45°) is not an energy minimum on two-dimensional-type Ramachandran potential energy surfaces (E = E{φ, ψ}). Theoretical investigations were performed on several single-amino-acid diamides such as For-Gly-NH2, For-L-Ala-NH2, Ac-L-Ala-NHMe, and For-L-Val-NH2 containing amino acid residues (e.g., Ala) which can often be found in helices as shown by X-ray data analysis of globular proteins. The current ab initio [self-consistent field (SCF)] results (based on four different basis sets [3-21G, 4-21G, 4-21G*, and 6-31G*]) presented point toward an intrinsic (i.e., non-environmental-assisted) stability of the right-handed helical subconformation of a simple amino acid diamide if the residue contains a polar side chain. Such is the case for a serine derivative when its (SINGLE BOND)CH2OH side chain is favorably oriented. For the For-L-Ser-NH2 model compound two slightly different right-handed helical backbone conformations were determined. Depending on the relative orientation of the side chain, the conformational monomer of the 310 helix (a sharper helical structure with an [i, i + 3]-type H-bond network) as well as the building block of the “standard” α-helix (the regular helical structure with an [i, i + 4]-type H-bond network) were determined computationally by geometry optimization. © 1997 John Wiley & Sons, Inc.
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    Cloppa RPA-AM1 analysis of the anisotropy of NMR 1J(XY) coupling tensors in Me3XY compounds (X = 13C, 29Si, 119Sn, 207Pb; Y = 19F, 35Cl) (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 823-833 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work, the CLOPPA approach is extended to allow the bond-contribution analysis of the anisotropic part, ΔJ, of the indirect nuclear spin-spin coupling tensor, J. As an example this method is applied to study the role played by the X-Y bond, its antibonding orbital, and the Y lone pairs in determining the Fermi contact-spin dipolar cross contribution to Δ1J(XY) in compounds of type Me3X(SINGLE BOND)Y (X = C, Si, Sn, Pb; Y = F, Cl). That contribution is found to be the main one, except for × = Pb, in this series of compounds. Calculations are carried out using semiempirical AM1 ground-state wave functions. © 1997 John Wiley & Sons, Inc.
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    Density-gradient analysis for density functional theory: Application to atoms (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 835-845 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present an analysis of local or semilocal density functionals for the exchange-correlation energy by decomposing them into their gradients rs (local Seitz radius), ζ (relative spin polarization), and s (reduced density gradient). We explain the numerical method pertaining to this kind of analysis and present results for a few atoms and ions. The atomic shell structure is prominent, and only the ranges 0 〈 rs 〈 10 and 0 〈 s 〈 3 are important. The low-density and large-gradient domains, where the approximations for the exchange-correlation energy are least trustworthy, have very little weight. © 1997 John Wiley & Sons, Inc.
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    The effect of an electric field on the vibrational frequency of CN (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 859-863 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio calculations are used to compute the change in the vibrational frequency of CN with an applied electric field aligned parallel to the bond axis. The effect of the field on the CN- vibrational frequency is of the same magnitude as for CN, but in the opposite direction. These results are compared to previous results for CO. © 1997 John Wiley & Sons, Inc.
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    Conductivity in polyacetylene. IV. Ab initio calculations for a two-site model for electron transfer between allyl anion and allyl (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 847-857 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electron exchange between allyl molecules is studied using quantum chemical ab initio methods in order to model interchain electron transfer (ET) in polyacetylene. The reaction path, reorganization energy for ET (λ), and the electronic factor (Δ) are calculated using the UMP2, CASSCF, CASPT2, and CASSI methods. Changes in bond lengths are very small and their contribution to the internal reorganization energy almost negligible. Only changes in the bond angle leave significant contributions to the reorganization energy. The calculated potential energy surfaces can be represented as interacting parabolic-well potentials only in the case of CASSI. The UMP2, CASSCF, and CASPT2 methods give the localization of the electron even in the symmetric case and incorrect energy surfaces, with a cusp at the symmetry point. The electronic factor Δ is calculated using the two different methods, Koopmans' theorem and CASSI, with the same basis set. They are quantitatively very close for all intermolecular distances under study. However, Δ is sensitive to the basis set and cannot be calculated accurately in the present case. © 1997 John Wiley & Sons, Inc.
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    Theoretical investigation of the rates of electron transfer processes Q-I + QII → QI + Q-II and Q-I + Q-II → QI + Q2-II in photosynthesis (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 865-879 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A theoretical investigation on the rates of electron-transfer processes Q-I + QII → Q-I + Q-II and Q-I + Q-II → QI + Q2-II was carried out by using the Marcus theory of long-range electron transfer in solution. The molecular reorganizational parameter λ, the free-energy change ΔG0 for the overall reaction, and the electronic matrix element HDA for these two processes were calculated from the INDO-optimized geometries of molecules QI, QII, and histidine. QI and QII are plastoquinones (PQ) which are hydrogen-bonded to a histidine each, and the two histidines may or may not be coordinated to a Fe2+ ion. The plastoquinone representing QI is additionally flanked by two peptide fragments. Each of the species (Pep)2QI · His and His · QII has been considered to be immersed in a dielectric continuum that represents the surrounding molecules and protein folds. INDO calculations confirm the standard reduction potential for the first process (calculated 0.127 V; observed 0.13 V) and predict a midpoint potential of 0.174 V for the second process at 300 K at pH 7 (experimental value remains uncertain but is known to be close to 0.13 V). The plastoquinone fragment carries almost all the net charge (about 95.7%) in [PQ · His]- and the net charge in [PQH · His]-. The electron is transferred effectively from the plastoquinone part of [(Pep)2QI · His]- to the plastoquinone moiety of QII · His in the first step and to the plastoquinone fragment of HisH+ · Q-II in the second step. Therefore, we made use of the formula for the rate of through-space electron transfer from QI to QII (and to Q-II). The plastoquinones are, of course, electronically coupled to histidines, and the transfer is, in reality, through the molecular bridge consisting of histidines and also Fe2+. The through-bridge effect is inherent in our calculation of ΔG0, HDA, and the reorganization parameter λ. We investigated the correlation between half-times for the transfer and (D-1op- D-1s), where Dop and Ds are, respectively, optical and static dielectric constants of the condensed phase in the vicinity of the plastoquinones. We found that with reasonable values of Dop (2.6) and Ds (8.5) the experimental rates are adequately explained in terms of transfers from the plastoquinone moiety of QI to that of QII. The t1/2 values calculated for the two processes are 247 and 472 μs in the absence of Fe2+ and 134 and 181 μs in the presence of Fe2+. These are in good agreement with the observed values which are ≈ 100 and ≈ 200 μs when Fe2+ is present in the matrix and which are known to be almost twice as large when the Fe2+ is evicted from the matrix. The present work also shows that the Marcus-Hush theory of long-range electron transfers can be successfully applied to the investigation of processes occurring in a semirigid condensed phase like the thylakoid membrane region. © 1997 John Wiley & Sons, Inc.
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    Design of an exchange functional with correct asymptotics (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 891-898 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Knowledge of asymptotic conditions on exchange allows for a better design of exchange energy expressions in density functional theory. By working inside an exchange-only framework, the fulfillment of such conditions by some of the most widely used exchange functionals is discussed. In turn, we propose a model expression which partially meets the energetics and asymptotics of both the exchange energy density and potential. Improvement upon the local spin density approximation without the use of generalized gradient corrections is also presented. Hartree-Fock orbitals are employed to build electron densities. © 1997 John Wiley & Sons, Inc.
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    Addendum to construction of linearly independent relativistic symmetry orbitals for finite double-point groups including time-reversal symmetry (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 929-933 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a previous article [J. Meyer, Int. J. Quantum Chem. 33, 445 (1988)], the formalism for the construction of linearly independent relativistic symmetry-adapted molecular basis functions under consideration of time-reversal symmetry was published. We present here an addition and correction of the application of time reversal on the construction. This new theory is now applicable to all double-point groups, including the icosahedral groups not considered so far. © 1997 John Wiley & Sons, Inc.
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    Correlation entropy of the H2 molecule (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 935-941 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Correlation of a quantum many-body state makes the one-particle density matrix nonidempotent. Therefore, the Shannon entropy of the natural occupation numbers measures the correlation strength on the one-particle level. Here, it is shown how this general idea of a correlation entropy must be adapted for two-electron systems in view of conservation laws which mix Slater determinants even in the noninteracting limit. Results are presented for the correlation entropy s of H2 as a function of the nucleus-nucleus separation R. In the ground state, the entropy of the spatial factor of the wave function maximizes 1.7 bohr beyond the Coulson-Fischer separation. The role of the correlation entropy in density functional theory is also discussed. © 1997 John Wiley & Sons, Inc.
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    Optimized Gaussian basis sets for use with relativistic effective (core) potentials: K, Ca, Ga—Kr (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 943-952 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Correlation-consistent valence basis sets were developed for the third-row main block elements (K, Ca, Ga - Kr) for use with relativistic effective core potentials. These basis sets are somewhat larger than double-zeta in size, with polarization functions, and are balanced for use in both Hartree-Fock and correlation calculations. Spin-orbit splittings for atoms and molecules are calculated and compared to experiment. These calculations use the approximate spin-orbit operator from the relativistic effective core potentials. The use of these results in the calculation of accurate thermochemical data is discussed. © 1997 John Wiley & Sons, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.
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    An ab initio study of the structure, dissociation energy, and heat of formation of Na2S (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 953-957 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The equilibrium geometries and fundamental frequencies of Na2S are calculated at HF, MP2(FC, FU), and MP3 with the 6-31G(d) basis set and at HF and MP2(FC, FU) with the 6-31G(d) basis set, respectively. The total energy at MP2(FU)/6-31G(d)-optimized geometry is computed at MP4 with 6-311G(d, p), 6-311 + G(d, p), and 6-311G(2df, p), at QCISD(T)/6-311G(d, p), and at MP2/6-311G(3df, 2p) levels, respectively. The dissociation energy, the atomization energy, and the heat of formation for Na2S are evaluated using the G1 and G2 models. The calculated results indicated that Na2S in its ground state was a bent structure (C2v). Electron correlation corrections on the bending angle are very significant. The equilibrium geometrical parameters are Re(Na-S) = 2.45 Å and ∠Na-S-Na = 111.13° at the MP2(FU)/6-31G(d) level. The theoretically estimated dissociation energy, total atomization energy, and heat of formation are 67.07, 117.55, and 0.35 kcal mol-1, respectively, at 298.15 K. © 1997 John Wiley & Sons, Inc.
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    Theoretical studies on local anesthetics: Procaine, lidocaine, tetracaine, bupivacaine, and dibucaine - neutral and monoprotonated (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 959-980 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular basis of the pharmacological action of tertiary amine local anesthetics (LA) is still unclear. However, there is experimental evidence that the LA penetrates into the axon as a neutral form and acts in the charged form from the intracellular phase. In this work we report quantum chemical semiempirical results for the neutral and monoprotonated forms of procaine, lidocaine, tetracaine, bupivacaine, and dibucaine. All geometries have been fully optimized with the AM1 Hamiltonian. Solvent effects were included at the self-consistent reaction field (SCRF) approximation. We have found that the most stable conformers of positively charged LA agents are all characterized by intramolecular H-bond formation involving the protonated amine groups. INDO/S-CIS calculations have revealed that the gas-phase absorption spectra of LAs result from the superposition of the spectra of the ring π system and the carbonyl, in a large extent perturbed by intramolecular charge transfer (CT). For all studied LAs, the benzene B2u bands are very weak and the benzene B1u bands gain intensity due to symmetry breaking. Formation of intramolecular H bond strongly affects the carbonyl CT bands. On the other hand, the spectrum of dibucaine is dominated by the quinoline π system. © 1997 John Wiley & Sons, Inc.
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    Structure and energy of the positively ionized water clusters (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 981-990 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Geometry optimization of small (H2O)n+ clusters (n ≤ 4) at the UHF/4-31 + + G** level indicates that the cations consist of two fragments: the OH radical and the H2n-1 O+n-1 ion. The latter can be considered as a thermodynamically stable combination of a distorted H3O+ ion and (n-2) H2O molecules. The H bond between the fragments becomes weaker with increasing cluster size. Extrapolation of the adiabatic ionization potentials calculated for the (H2O)n oligomers (n ≤ 4) at the MP2 level to an infinite cluster size provides the value of approximately 8.7 eV, which can be presumably necessary for the ionization of liquid water in a vacuum. © 1997 John Wiley & Sons, Inc.
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    Calculations of the structure and electronic properties of extended polar hydrocarbons (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 991-996 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure and nonlinear optical potential of a series of polar unsaturated hydrocarbons containing the electron-donating heptafulvene ring and electron-attracting pentafulvene ring have been explored in terms of their first hyperpolarizabilities using a semiempirical sum-over-states and time-dependent coupled Hartree-Fock approach. Both methods predict that the hyperpolarizabilities of these simple hydrocarbons are substantial and exceed those found for many extended conventional donor-acceptor systems. © 1997 John Wiley & Sons, Inc.
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    Time-evolution operator for a forced parametric oscillator (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 125-135 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We apply an algebraic technique to describe the evolution of a parametric harmonic oscillator forced by a constant quartic potential. As the first step, we make use of iterative Bogolubov transformations (IBT) to incorporate information from the anharmonic part of the interaction in a nonperturbative form, yielding a unitary time-evolution operator. Later on, we make use of first-order perturbation theory to deal with that part of the interaction which was not incorporated previously. We show numerically that the resulting time-evolution operator is closer to unitarity than is the one obtained if no IBT is applied. The quantum fluctuations of position and momentum are evaluated for “the ground” state. Squeezing and correlation effects are observed. © 1997 John Wiley & Sons, Inc.
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    Single-reference CCSD approach employing three- and four-body CAS SCF corrections: A preliminary study of a simple model (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 137-151 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The idea of correcting the single-reference coupled cluster (CC) method truncated at the pair cluster level (CCSD) by means of three- and four-body corrections coming from some external source [J. Paldus, J. Čížek, and M. Takahashi, Phys. Rev. A 30, 2193 (1984); J. Paldus and J. Planelles, Theor. Chim. Acta 89, 13 (1994)] is explored at the ab initio level using the CAS SCF wave functions as a source of the triply and quadruply excited cluster amplitudes. The method (referred to as CCSD-CAS) is applied to three simple systems based on minimum basis set and double-zeta models of the BH molecule, in which we continuously vary, respectively, (i) the two electron repulsion, (ii) the electronic charge, and (iii) the internuclear separation in order to explore the performance of the method in quasi-degenerate situations. Both the energies and the higher than pair cluster amplitudes are compared with the corresponding exact full configuration interaction (FCI) results. The relative importance of the three- and four-body cluster components is also examined. In all cases considered, the CCSD-CAS method provides the best result. © 1997 John Wiley & Sons, Inc.
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    On the restricted step method coupled with the augmented Hessian for the search of stationary points of any continuous function (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 153-165 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In any optimization using the augmented Hessian technique, the step is not restricted to any length. Since the restriction of the step at each iteration is very important in order to achieve good convergence, we present a coupled method such that the augmented Hessian automatically gives both the adequate length of the step and the correct Hessian structure. The method is showed for the minima and saddle points of any order. © 1997 John Wiley & Sons, Inc.
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    Statistical electron densities (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 85-93 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is known that in numerous interesting systems one-electron states appear with a multifractal internal structure. Physical intuition suggests, however, that electron densities should be smooth both at atomic distances and close to the macroscopic limit. Multifractal behavior is expected at intermediate length scales, with observable nontrivial statistical properties in considerably, but far from macroscopically sized clusters. We have demonstrated that differences of generalized Rényi entropies serve as relevant quantities for the global characterization of the statistical nature of such electron densities. Asymptotic expansion formulas are elaborated for these values as functions of the length scale of observation. The transition from deterministic electron densities to statistical ones along various lengths of resolution is traced both theoretically and by numerical calculations.    © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 85-93, 1997
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    Adiabaticity and gauge transformations for an oscillator coupled to a single-mode field (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 111-119 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The components of the Floquet wave function of an oscillator in various representations are correlated. The transformation from length to velocity gauge can be viewed as a change from a diabatic to an adiabatic representation in the field variable. This is shown in three different ways.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 111-119, 1997
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    The optimized effective potential method of density functional theory: Applications to atomic and molecular systems (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 95-110 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using the optimized effective potential method in conjunction with the semianalytical approximation due to Krieger, Li, and Iafrate, we performed fully self-consistent exact exchange-only density functional calculations for diatomic molecules with a fully numerical basis-set-free molecular code. The results are very similar to the ones obtained with the Hartree-Fock approach. Furthermore, we present results for ground states of positive atomic ions including correlation contributions in the approximation of Colle and Salvetti. It is found that the scheme performs significantly better than do conventional Kohn-Sham calculations.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 95-110, 1997
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    Energies of dipole-bound anionic states (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 183-191 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dipole-bound anionic states of CH3CN, C3H2, and (HF)2 were studied using highly correlated electronic structure methods and extended one-electron basis sets. The electron detachment energies were calculated using the coupled cluster method with single, double, and noniterative triple excitations. Geometrical relaxation of the molecular framework upon electron attachment and the difference in the harmonic zero-point vibrational energies between the neutral and the dipole-bound anionic species were calculated at the MP2 level of theory. We demonstrate that the dispersion interaction between the loosely bound electron and the electrons of the neutral molecule is an important component of the electron binding energy, comparable in magnitude to the electrostatic electron-dipole stabilization. The geometrical relaxation upon electron attachment and the change in the zero-point vibrational energy is important for the weakly bound HF dimer. The predicted values of the vertical electron detachment energies for the dipole bound states of CH3CN and C3H2 of 112 and 188 cm-1, respectively, are in excellent agreement with the recent experimental results of 93 and 171±50 cm-1, respectively. For (HF)2-, the predicted value of adiabatic electron detachment energy is 396 cm-1, whereas the experimental vertical detachment energy is 508±24 cm-1. The possibility of formation of the neutral dimer in an excited vibrational state is considered.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 183-191, 1997
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    Accurate density-functional calculations on large systems (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 193-203 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Efforts to compute accurate all-electron density-functional energies for large molecules and clusters using Gaussian basis sets are reviewed and their use in fullerene science described. The foundation of this effort, variational fitting, is described first. When discovered experimentally, C60 was naturally assumed to be particularly stable, but local-density-functional calculations showed that C60 is quite unstable relative to the higher fullerenes and graphene (a single sheet of graphite). In addition to raising questions about the relative abundance of the various fullerenes, this work conflicted with the then state-of-the-art density-functional calculations on crystalline graphene. Now high accuracy molecular and band structure calculations are in fairly good agreement with each other and experiment. These calculations clearly demonstrate that each of the 12 pentagons, which are necessary to close a fullerene, is best viewed as a rather high-energy, more than 2 eV, defect in a graphene sheet. The effect of the heptagon, the second most common defect in fullerene materials, is described. Most recently, we have developed accurate, variational gradient-corrected forces for use in geometry optimization of clusters and in molecular-dynamics simulations of friction. The gradient-corrected optimized geometry of C60 is given.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 193-203, 1997
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    Density-functional investigation of some decomposition routes of methyl nitrate (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 205-210 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two density-functional methods, B3/LYP/6-31+G(d) and B3/PW91/6-31G(d, p) have been used to investigate some possible decomposition pathways for methyl nitrate. Two likely ones were found to be (a) loss of NO2, followed by eventual rearrangement to H2C(SINGLE BOND)OH, and (b) formation of H2C(DOUBLE BOND)O and HONO. The initial energy requirement for each process is about 40 kcal/mol, and the second is exothermic, ΔH=-16 kcal/mol of H3C(SINGLE BOND)ONO2. The B3/LYP procedure is found to underestimate the H3CO(SINGLE BOND)NO2 and H3C(SINGLE BOND)ONO2 dissociation energies by about 6 kcal/mol.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 205-210, 1997
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    The role of the Jahn-Teller distortions on the structural, binding, and magnetic properties of small Fen clusters, n≤7 (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 223-230 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Small clusters of iron atoms, up to heptamers, were studied by density functional theory. The calculations performed were all-electron and both local and gradient-dependent potentials were used. Most of the symmetric or compact structures show degenerate electronic states which are stabilized, through Jahn-Teller distortions, in lower symmetry or more open geometries. As the cluster size increases, the coordination numbers increase, the metal-metal bond strengths are reduced, and the equilibrium bond lengths are enlarged. This behavior accounts for the occurrence of high magnetic moments on the atomic sites, which are coupled ferromagnetically.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 223-230, 1997
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    Studies of chemical hardness and chemical potential on isomers and hardness profiles of hydrogen-bonded systems (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 231-242 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the present investigation, chemical hardness and electronic chemical potential for isomers of different molecules were studied by taking into account the principle of maximum hardness. Different isomers of the molecules, XC(O)OX (X=F, Cl), C2H3NO, C2H2, and HCNC, were considered for the above investigation. In most of the cases, the chemical hardness was found to be a good indicator for predicting the most stable isomer and not the chemical potential. The hardness profiles of different configurations of the interacting systems, HF(DOTTED BOND)HCN, HF(DOTTED BOND)HCl, and CH3OH(DOTTED BOND)H2O hydrogen-bonded complexes, were studied. The extrema of the hardness profiles does not coincide well with the energy, but in some cases, the hardness profile follows the interaction path. The higher hardness-higher stability concept among different configurations of the hydrogen-bonded complexes are discussed.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 231-242, 1997
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    Ionized van der Waals systems: Structure and interactions (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 211-222 
    Details
    ISSN: 0020-7608
    Keywords: quantum chemistry ; weak interactions ; cationic van der Waals complexes ; cluster cations ; potential energy surfaces ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ions of molecular complexes with internal interactions partly of van der Waals type differ significantly from their neutral parent species in binding, structure, and dynamics. Information about such systems is still rather scarce, both experimentally and theoretically. The article discusses some aspects of the present knowledge concerning cationic dimers and trimers of the type RgnM+ with Rg denoting a rare-gas atom, and M, either a (diatomic) molecule or a rare-gas atom, in comparison with the neutral counterparts. In some more detail, potential energy surfaces (PESs) for the six lowest electronic states of ArHCl+ are reported, as obtained from multireference CI calculations with an extended Gaussian AO basis set. From the PESs, structural, energetical, and dynamical features are derived. For the cationic argon trimer Ar3+ in the electronic ground state, a detailed analysis of the PES, the mode couplings, and the classical internal dynamics is carried out, leading to a consistent picture of a floppy molecular aggregate with rapid energy exchange between internal degrees of freedom and early onset of classical chaos with increasing energy.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 211-222, 1997
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    An LDA calculation of the conformation and electronic structure of polytetrafluoroethylene (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 243-246 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A density functional calculation of the structural and electronic properties of polytetrafluoroethylene systems with several different dihedral angles is presented using two different local density approximations, the Gáspár-Kohn-Sham and the Perdew-Zunger. All the geometrical parameters were optimized simultaneously for the stable conformation. The torsional potential curve shows an absolute minimum at the dihedral angle of 163.7°, corresponding to a slightly deformed planar zigzag conformation. Other two distinct local minima for the quasi-stable helical conformation are found at the gauche form. The calculated valence and conduction bands are discussed and compared with other theoretical calculations and experiment.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 243-246, 1997
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    Computation of geometries and frequencies of singlet and triplet nitromethane with density functional theory using Gaussian-type orbitals (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 263-269 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The results of computational studies of the structures, energies, dipole moments, and infrared spectra for singlet and triplet nitromethane are presented. Five different hybrid (B HandH, BHandHLYP, B3LYP, B3P86 and B3PW91), local (SVWN), and nonlocal (BLYP) density functional theory (DFT) methods were used in this study with various sizes of a Gaussian-type basis set. The obtained results were compared to Hartree-Fock (HF), second-order Møller-Plesset (MP2), and multiconfiguration self-consistent-field (MCSCF) ab initio calculations, as well as to the experimental results. The suitability of DFT methods to correctly reproduce experimental results is discussed.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 263-269, 1997
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    Computation of some ionization potentials for second-row elements by ab initio and density functional theory methods (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 255-261 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four ionization potentials of elements from the second row of the periodic table were computed with ab initio (HF, MP2, MP3, MP4, QCISD, G1, G2, and G2MP2) and density functional theory (DFT) (B3LY, B3P86, B3PW91, XALPHA, HFS, HFB, BLYP, BP86, BPW91, BVWN, XAPLY, XAP86, XAPW91, XAVWN, SLYP, SP86, SPW91 and SVWN) methods. In all of the calculations, a large 6-311++G(3df, 3pd) Gaussian-type basis set was used. The computed values were compared to experimental results, and the suitability of these ab initio and DTF methods for computing atomic ionization potentials was discussed. It was found that G2 will produce ionization potentials that are indistinguishable from the experimental values. Hybrid B3LYP and nonlocal BLYP will generate very good ionization potentials. For larger atoms, SLYP and SPW91 will compute ionization potentials that are of G2 quality.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 255-261, 1997
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    Comparative AM1 study of the electronic structure of etiocholanes (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 249-254 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Etiocholanes are metabolites of androstenedione (4-androsten-3,17-dione) and testosterone (17β-hydroxy-4-androsten-3-one). These compounds are produced by the action of 5-reductases which break the π double bond of the androstenes at C4 and C5. The most important etiocholanes are 5β-androstanedione (etiocholanedione), 3α-hydroxy-5β-androstan-17-one (etiocholanolone), 3β-hydroxy-5β-androstan-17-one (epietiocholanolone), and 17β-hydroxy-5β-androstan-3-one (5β-dihydrotestosterone; 5βDHT). Among their most important biological effects are depression of the central nervous system, relaxation of smooth muscle, and stimulation of sexual behavior. The intent of the present study is a determination of the effects of carbonyl and hydroxyl groups at C3 and C17 on the electronic structure of these androgens, in an attempt to gain some insight into their biological action. All calculations were of the semiempirical AM1 type. The decrease of enthalpy caused by an hydroxyl group was found to be twice that of a carbonyl group. The effect of two groups was found to be additive. Carbonyl groups on the other hand led to an increase of dipole moment and of the electrostatic charges on neighboring carbons that were higher than those produced by hydroxyl groups. Carbonyl groups at C17 pushed the highest occupied molecular orbital (HOMO) to higher energy whereas a carbonyl at C3 had little or no effect. However, in mono and di-keto structures, both HOMO and lowest unoccupied molecular orbital (LUMO) were located as expected closer to the carbonyl group. Etiocholanedione, a diketo structure, showed degeneracy of frontier orbitals with its related HOMO-1 and LUMO+1. Structures with mono-hydroxyl or di-hydroxyl functional groups showed the lowest HOMO values; the highest LUMO values and quasi degeneracy of HOMO-1 and LUMO+1. The HOMO and LUMO of etiocholane and for the mono and di-hydroxyl structures were observed diffused throughout the molecules in a “sausagelike” or “ribbonlike” fashion. These results might explain some metabolic steps. Likewise, the difference of intermolecular forces, i.e., dipole moments and charges displayed by the carbonyl and hydroxyl groups, might help to elucidate some biological effects.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 249-254, 1997
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    Coupling-constant dependence of atomization energies (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 285-295 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The local spin-density (LSD) functional and Perdew-Wang 91 (PW91) generalized gradient approximations to atomization energies of molecules are investigated. We discuss the coupling-constant dependence of the atomization energy and why exchange errors of the functionals are greater than exchange-correlation errors. This fact helps to justify hybrid schemes which mix some exact exchange with density functional approximations for exchange and correlation. It is shown that the biggest errors in the atomization energies occur when there is a strong interaction between different electron pairs, which vanishes upon atomization. We argue that the amount of exchange character of a molecular property, such as the atomization energy, depends on the property itself. We define an exact mixing coefficient b, which measures this exchange character, and show that both LSD and PW91 typically overestimate this quantity. Thus, nonempirical hybrid schemes which approximate this quantity by its LSD or PW91 value typically do not improve the exchange-correlation energy.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 285-295, 1997
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    QR-SCMEH-MO calculations on lanthanide systems. IV. The [SmCp*]4 cluster (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 297-300 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Additional calculations via the quasi-relativistic self-consistent-modified extended Hückel-MO method (QR-SCMEH-MO) were conducted on the model cluster [SmCp*]48+ and the real [SmCp*]4(N2H2)2(N2H3) 4(NH3)2 cluster. It is shown that this is no trivial problem, owing to correlation arising from the electron repulsion among open shells, plus the close proximity of open- and closed-shell configurations. An acceptable result is shown to be sensitive to spin-orbit splitting and electron-pairing interactions.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 297-300, 1997
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    The distribution of polynuclear aromatic hydrocarbons between aquatic plants and sediments (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 271-283 
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    ISSN: 0020-7608
    Keywords: acropetal ; adsorption ; aquatic plants ; polynuclear aromatic hydrocarbons ; sediments ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Saturation phenomena for the uptake of polynuclear aromatic hydrocarbons (PAHs) by rooted aquatic plants were observed in both field and laboratory experiments. From these data, a Langmuir adsorption model was derived and was shown to describe the assimilation of sediment PAHs by aquatic plants at low-sediment PAH concentrations. The low-concentration restrictions were relaxed by using an empirical Freundlich model. This permitted the specification of equilibrium constants, relative rate constants for adsorption and desorption, and saturation levels, and it provided a realistic description of the acropetal mobilization of sediment PAHs by rooted aquatic macrophytes. The growth of aquatic plants was found to be inhibited by sediment PAHs, but at concentrations several orders of magnitude above the corresponding threshold effect levels for aquatic animals. The effects of the acropetal transport of sediment PAHs into the above-soil portions of aquatic plants merits further investigation because of the possibility of an enhanced availability of these carcinogens to associated aquatic food webs. In addition, these results may suggest pathways for bioremediation of the impact of PAHs on associated biota.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 271-283, 1997
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    Geometry optimization of polymers by the elongation method (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 301-323 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Theoretical studies on the electronic and the geometrical structures for various molecules by the molecular orbital or the density functional theory have recently been developed and applied widely under the progress of computer technologies. At present, it is possible to carry out a theoretical investigation on electronic properties for small molecules at the Hartree-Fock and the post-Hartree-Fock levels by the improvement of advanced program packages. However, it is difficult to perform the theoretical calculations on electronic structures for large polymers with the aperiodic sequence of molecular segments, because the theoretical treatment of random systems has not yet been established. We recently proposed the elongation method as a useful theoretical approach to obtain the electronic states of any polymers without the periodic geometry of molecular fragments. In the previous works, the reliability of our treatment has been shown by the application to many polymers under single-point calculations with fixed molecular geometry. Thus, as the next step of our study, an attempt for the geometry optimization of large polymers by the elongation method was made in this work. As the first samples of geometry optimization, the periodic polymers of polyethylene, polyacetylene, and polyglycine were examined. Also, as the second samples, the locally aperiodic polymers of polyacetylene with local defects of positively and negatively charged solitons were tested. Total energies, optimized geometries, and electron densities were checked by those obtained from the conventional molecular orbital method.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 301-323, 1997
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    Molecular orbital approach to the Peierls instability in polyenes and its application to model crystals of charge-transfer complexes (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 325-336 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have already proposed a convenient method to estimate the magnitude of the Peierls instability in finite one- and two-dimensional (1D and 2D) polyenes from the viewpoint of orbital symmetry [J. Chem. Phys., 103, 9726 (1995)]. This treatment is applied to a model system for charge-transfer complexes, in which the unpaired electron is occupied in a molecule, generating a half-filled energy band by intermolecular interaction. As the first step, a model molecular crystal composed of ethylene anion (or cation) molecules is treated to confirm the applicability of our formulas for 2D polyene. It is clearly shown that molecules in a crystal are structurally distorted to gain the energetic stabilization within the 1D structure, while they are rearranged in a regularly equidistant structure under strong interchain interaction. This treatment would provide insight into the relationship between the crystal structure of charge-transfer complexes and its electronic property.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 325-336, 1997
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    Heterogeneous reactions over fractal surfaces: A multifractal scaling analysis (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 337-350 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Monte Carlo simulations of Eley-Rideal (ER) mechanisms with fixed and varying sticking probabilities, p, as well as a three-step catalytic reaction (TCR) over fractal surfaces were performed to examine the morphological effect on the above-mentioned reactions. The effect of decay and enhancing profiles on the reaction probability distribution (RPD) for the ER reaction as well as effects of a varying probability of reaction steps on the normalized selectivity distribution (NSD) for the three-step reaction were then analyzed by multifractal scaling techniques. For ER with a fixed sticking probability, a small p value tends to yield homogeneous RPD. For ER with a varying sticking probability, the RPD is revealed to be spatially uniform at fast decay and rather concentrated at a faster enhancing rate. For the three-step reaction, a large dimerization/isomerization ratio increases the position distinction among active sites as the adsorption probability equals 1. At a small adsorption probability, the dimerization/isomerization ratio causes no effect on the NSD. Heterogeneity of surfaces as reflected in the multifractal analysis will also be discussed.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 337-350, 1997
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    Davydov solitons in proteins Contribution to the Proceedings of the 2nd Congress of the International Society for Theoretical Chemical Physics at New Orleans Louisiana April 9-13 1996. (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 351-377 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism for energy and signal transport in proteins as suggested by Davydov is discussed. The idea is based on a coupling of amide-I oscillators to acoustic phonons in a hydrogen-bonded chain. Results as obtained with the usually used ansätze are discussed. The quality of these states for an approximate solution of the time-dependent Schrödinger equation is investigated. It is found that the semiclassical ansatz is a poor approximation, while the more sophisticated |D1〉 state seems to represent the exact dynamics quite well. Calculations at a temperature of 300 K for one chain, as well as for three coupled ones (as they are present in an α-helix), are presented and discussed. From the calculations, it is evident that Davydov solitons are stable for reasonable parameter values at 300 K only for special initial excitations close to the terminal sites of the chain. However, for soliton formation, it is not necessary that the initial excitation occurs at the chain end which has its C(DOUBLE BOND)O group directly coupled to the lattice as it is the case for T=0 K. At higher temperatures, solitary waves can be formed from both chain ends. Since the model for temperature effects used was criticized from the theoretical point of view, we suggest an improved theory for temperature effects. Finally, we discuss recent experimental findings which indicate that normal modes describing the N(SINGLE BOND)H stretch and its coupling to the hydrogen bonds should be considered in addition to the amide-I vibration.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 351-377, 1997
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    Outlines of a general framework of cancer initiation in the cell (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 379-385 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: According to the central dogma of molecular biology, information flows in the living cell from DNA through RNA to proteins. Therefore most investigations of cancer initiation try to explain these effects by carcinogen binding to, or radiation hits on, DNA which lead to the first steps of the malignant transformations. On the other hand, recent detailed theoretical investigations have shown that proteins are good disordered hopping conductors (their conductivity is in the order of good conducting amorphous glasses). Their conductivity can be substantially influenced by binding of chemicals or by the effects of radiation if they cause conformational changes (as recent calculations have shown). These effects can also destroy bonds or generate new bonds in proteins. If the affected proteins are regulatory proteins, they can be inactivated in both ways. Namely, on the basis of Warburg's experiments, one can postulate that if the hindrance of oxygen metabolism leads to fermentation, and with it to the malignant transformation, this means also the hindrance of electron flow in the Szent-Györgyi-Krebs cycle. In other words the hindrance of electron transport in this cycle most probably has the same effect as the lack of oxygen, which in this way most probably leads again to a malignant transformation. Finally the inactivation of regulatory enzymes can influence also the regulation of the expression of oncogenes. If in this way oncogenes become overactivated (or antioncogenes become inactive), the changes started by the inactivation of regulatory enzymes become hereditary. It seems that if we look at the cell as a complicated self-regulatory system, primary changes both at their DNA or regulatory protein molecules caused by external agents can disturb its self-regulation and transform it in this way into another stationary, possibly precancerous, state.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 379-385, 1997
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    Computer simulation of DNA sequential correlations (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 387-392 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To obtain new insight into the nature of the correlations in distributions of nucleotides in DNA sequences, an efficient algorithm is presented by means of which one can generate nucleotide sequences with prescribed correlational properties. It is demonstrated in the case of human T-cell receptor beta chain gene segment that by extracting a finite number of parameters from the natural sequence one can generate artificial sequences which reproduce the correct correlational properties. It is shown how the apparent long-range correlations, or - what is equivalent - the 1/f form of the spectral density result due to the arrangement of DNA segments with different functional roles which also differ in composition in terms of nucleotide classes. This approach enables one to get under control the impact of statistical fluctuations which represent a major obstacle in the analyses of finite natural sequences.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 387-392, 1997
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    Two approaches to stochastic rate theory (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 393-401 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A comparison is made between two approaches to a Kramers-type reaction rate theory. The usual one is based on a linear coupling model between a particle and the medium oscillators. Use is made of two different separable reaction coordinates in the absence and presence of coupling, respectively. A more general model consists of assuming an arbitrary (nonlinear) coupling between the reactant and medium, making use of a single (curvilinear) reaction coordinate of the entire many-dimensional system (reactant+medium). A comparison with the exact dynamic rate theory is made, showing its equivalence with the generalized stochastic theory.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 393-401, 1997
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    Comprehensive strategy for the calculation of overlap integrals with Slater-type orbitals (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 881-889 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A strategy is presented for the calculation of two-center overlap integrals over Slater-type orbitals. Displaced orbitals are expanded in spherical harmonics with Löwdin α-functions as coefficients. The exponentials in the α-functions are expanded, leading to representation in terms of stored E and F matrices. For a given precision, the number of terms needed for each orbital for a specified harmonic, and its displacement multiplied by its screening constant, is predetermined and stored. A survey of these data is presented. The one-dimensional integration needed for the overlap is done by Gauss-Legendre numerical integration over the interior region and analytically over the exterior. Complete stability is achieved and excellent results obtained. Implications for all multicenter molecular integrals are apparent. © 1997 John Wiley & Sons, Inc.
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    Calculation of NMR shielding tensors based on density functional theory and a scalar relativistic Pauli-type Hamiltonian. The application to transition metal complexes (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 899-918 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article deals with the calculation of the shielding tensor of nuclear magnetic resonance (NMR) spectroscopy based on a scalar relativistic two-component Pauli-type Hamiltonian. A complete formulation of the method within the framework of the gauge including atomic orbitals (GIAO) is given. Further, an implementation, based on density functional theory (DFT) is presented. The new method is applied to the 17O shielding in transition-metal oxo complexes [MO4]n- (M = Cr, Mo, W; Mn, Tc, Rh; Ru, Os) and to the metal chemical shift in transition-metal carbonyls M(CO)6 (M = Cr, Mo, W). This represents the first calculation of heavy-element shifts that is based on a relativistic first-principle quantum mechanical method. The inclusion of relativity is crucial for a proper description of ligand and metal shieldings in 5d complexes, but it is also important in 4d complexes. Limitations of the method, among them the neglect of the spin-orbit coupling, are discussed in detail. © 1997 John Wiley & Sons, Inc.
    Additional Material: 6 Tab.
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  • 88
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    Substitution effects by SCF and Hückel theory (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 919-927 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A basic ansatz for the dipole moment has been programmed in Hückel theory and used to calculate some field-dependent properties. This is related to fundamental properties of shaped potentials rather than a good representation of real molecular properties. Limiting values may be meaningful and have been compared with semiempirical and SCF calculations. Coulson and Longuett-Higgins-style Coulomb integral perturbations were calculated. These give clear molecular design indications which are partially backed up by small-scale SCF calculations, using perturbations of the nuclear charge. This work is not intended to be comparable to good ab initio calculations but to point to rough and ready geometrical models of electrical susceptibility. © 1997 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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  • 89
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    Electrostatic medium effects and formal quantum structure-activity relationships in apomorphines interacting with D1 and D2 dopamine receptors (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 997-1002 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The binding of apomorphines (AM) to D1 and D2 dopamine receptors is analyzed through a formal quantum structure-activity relationship method. The calculations were carried out at the CNDO/2 level of the molecular orbital theory with a continuum representation of environmental effects. The results show that the D1 receptor affinity variation is related to the variation of the electron-donating capacity of a C atom of the hydroxylic region of apomorphines in a low-polarity medium. The N-chain probably interacts with a hydrophobic region of the receptor. It is also concluded that the poor results for the D2 binding affinity are explained by errors in the experimental measurements. Finally, it is proposed that future structure-activity relationship studies must be carried out for media of different polarities. © 1997 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 90
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    On alternant molecules with identical energy spectra: Isospectral molecules (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 167-169 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that if a pair of alternant molecules are isospectral (they have identical energy spectra) in the topological - Hückel - approximation they are also isospectral, taking into account the electron correlation. The proof is given in the AMO approximation using a Hubbard Hamiltonian. © 1997 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 91
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    Electron reorganization in chemical reactions: Pair population analysis along concerted reaction path of allowed and forbidden pericyclic reactions (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 171-176 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The recently proposed pair population analysis was applied to the study of electron reorganization in the course of chemical reactions. The studied reactions involved a series of pericyclic reactions, both forbidden and allowed, and attention was devoted mainly to the evaluation of the specific differences between the allowed reactions and the forbidden ones. It was demonstrated that while the mechanism of allowed reactions can be visualized as a simple cyclic shift of the bonds the electron reorganization in forbidden reactions is much more complex and involves the considerable changes in the character of the wave function during the process. © 1997 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 92
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    Electronic Resource
    Oscillators in one and two dimensions and ladder operators for the Morse and Coulomb problems (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 177-183 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We exhibit that the radial eigenfunctions of a 2D-harmonic oscillator (2DHO) may be regarded as 1D-harmonic oscillator (1DHO) matrix elements. From this simple fact and using as a starting point the ladder operators â± for 1DHO, we obtain ladder operators for 2DHO. Furthermore, by using the relationship between the Coulomb and Morse problems with a 2DHO, we are able to obtain the ladder operators for the former problems without explicitly recurring to the factorization method. Some uses of the technique presented are suggested. © 1997 John Wiley & Sons, Inc.
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  • 93
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    Electronic Resource
    Discrete variable representation method applied to the determination of rotation-vibration bound states of NO2 (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 199-211 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The discrete variable representation method is applied to the determination of the rotation-vibration energy levels of the fundamental electronic state of NO2. The Hamiltonian is expressed in Johnson hyperspherical coordinates and developed on a DVR basis for each internal coordinate, while parity-adapted linear combinations of Wigner functions are used to describe the rotational motion. The diagonalization of the Hamiltonian matrix is performed using the Lanczos algorithm for large symmetric and Hermitian matrices. Results for rovibrational states up to J = 11 for the first five vibrational energy levels are presented. © 1997 John Wiley & Sons, Inc.
    Additional Material: 2 Tab.
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  • 94
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    Internal rotation study of some sixfold barrier molecules (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 213-221 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular orbital calculations of sixfold barriers in nitromethane, methyl boron difluoride, and trifluoronitromethane were performed by various Hartree-Fock and electron correlation methods. In those calculations, staggered and eclipsed conformations are of primary concern. These results indicated that for CH3NO2 and CH3BF2 the staggered conformations are more stable, while CF3NO2 has a more stable conformation in an eclipsed form. Both conformations do not differ significantly, which may account for the low internal rotational barrier of each molecule. Values of the barrier calculated by the Møller-Plesset perturbation and the quadratic configuration interaction methods did not match the experimental results. However, better internal rotational barrier values of each molecule were observed when the improved better basis sets and the Hartree-Fock method were selected. © 1997 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 95
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    13-atom Ni-Al alloy clusters: Structures and dynamics (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 185-197 
    Details
    ISSN: 0020-7608
    Keywords: alloy clusters ; isomers ; homotops ; isomerization ; meltinglike transition ; surface melting ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structural and dynamical properties of model 13-atom NinAlm alloy clusters derived from a many-body potential are presented and discussed. Characterization of the structures corresponding to a given stoichiometric composition (i.e., chosen number of Ni and Al atoms) is carried out in terms of isomeric (geometric) forms and different distributions of the two types of atoms between the sites of a chosen isomer. We use the term homotops (“the same topography or geometry”) to label the structural forms that differ only by these distributions. The number and the energy spectra of the homotops are sensitive functions of the stoichiometric composition and isomeric form. Similarly to homogeneous clusters, alloy clusters undergo a solid-to-liquidlike transition as their energy is increased. Individual stages in the transition, such as isomerizations involving only surface atoms, isomerizations involving all atoms, surface melting (in a system as small as 13 atoms), and complete melting are identified and characterized. The actual occurrence of some or all of these stages in the meltinglike transition of a given cluster depends on the character of the energy spectra of its homotops, i.e., ultimately, on its stoichiometric composition. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 185-197, 1997
    Additional Material: 9 Ill.
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  • 96
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    Implementation of gradient formulas for correlated gaussians: He, ∞He, Ps2, 9Be, and ∞Be test results (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 223-235 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New formulas in the basis of explicitly correlated Gaussian basis functions, derived in a previous article using powerful matrix calculus, are implemented and applied to find variational upper bounds for nonrelativistic ground states of 4He, ∞He, Ps2, 9Be, and ∞Be. Analytic gradients of the energy are included to speed optimization of the exponential variational parameters. Five different nonlinear optimization subroutines (algorithms) are compared: TN, truncated Newton; DUMING, quasi-Newton; DUMIDH, modified Newton; DUMCGG, conjugate gradient; and POWELL, direction set (nongradient). The new analytic gradient formulas are found to significantly accelerate optimizations that require gradients. We found that the truncated Newton algorithm out-performs the other optimizers for the selected test cases. Computer timings and energy bounds are reported. © 1997 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 97
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    Electronic Resource
    Molecular and biomolecular electronics (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 237-238 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 98
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    Electronic Resource
    Introduction (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 1-5 
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    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes:    © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 1-5, 1997
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  • 99
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    Electronic Resource
    Force balance equations in inhomogeneous classical and quantal liquids (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 21-29 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Inhomogeneous liquids in the presence of an external potential are considered. Exact force balance equations are written explicitly for (a) the classical case with pairwise interactions and (b) the ground-state quantal case of fermions with a general interaction, which embraces the Coulomb repulsion for electrons. Illustrative examples are given in both cases (a) and (b). Finally, a link between (a) and (b) is forged by considering the case of ensembles of finite systems.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 21-29, 1997
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  • 100
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    Electronic Resource
    Evolution of atomic-molecular eigenchannels (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 31-33 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemical reactions - as well as other collision processes - proceed generally from input elements condensing into a transitional complex and then dissociating into new fragments. Viewing the complex formation as reciprocal to its fragmentation combines them into conjugate elements of a single process, namely the complex evolution from a compact to a fragmented form, as its radius of inertia expands. As the wave functions of an atomic electron resolve conveniently into their radial and spherical-harmonic elements, so do those of multiparticle complex resolve into radial and hyperspherical-harmonic parts. Their numerical integration becomes thus accessible without resort to independent-particle or perturbative approximations. This approach displays a complex progressive branching into fragmentation channels. Evidence from small prototypes has shown each branching step to involve only a modest subset of the infinite harmonics set.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 31-33, 1997
    Additional Material: 1 Ill.
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