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  • 1
    Electronic Resource
    Electronic Resource
    An ab initio configuration interaction study of the reaction between small lithium clusters (Li4, Li6) and H2 molecule (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 5533-5543 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A reaction path for the Li4+H2 interaction has been determined allowing for the relaxation and the reconstruction of the system. For various steps along the reaction path characterized by the given values of one or two geometrical parameters the full geometry optimization of the remaining variables has been carried out in the framework of the Hartree–Fock (HF) procedure. The configuration interaction (CI) energies for the optimal HF geometries in each step have been calculated using multireference diexcited (MRD-CI) procedure. The calculated dissociation energy for the molecular hydrogen is reduced from 103.6 to 19.6 kcal/mol in the presence of Li tetrameter. During the first stage of the reaction path referred as "dissociative chemisorption'' the geometry of the Li tetrameter does not change substantially. After dissociation of H2 the full reconstruction of the tetrameter takes place leading to a local minimum which is separated from the lowest minimum by a moderate barrier along the chosen reaction path. The stable compound has the form of deformed rhombus with two hydrogen atoms bridging two neighboring rhombus sides. The preliminary calculations using complete active space self-consistent field procedure followed by direct CI carried out for the Li6+H2 interaction in the C2v symmetry yield fairly stable three dimensional LI6H2 compound, which can be formed after passing an energy barrier of comparable size at the present level of calculation as that found for the Li4+H2 reaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460489
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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio predictions of structural and optical response properties of Na+n clusters: Interpretation of depletion spectra at low temperature (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 1427-1440 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We show that a comparison of the depletion spectra of Na+n (n=2–9,11,21) clusters recorded at low temperature and optically allowed transitions determined for the stable structures using ab initio methods accounting for electron correlation allows the assignment of the cluster geometry to the measured features. Due to the large mobility of atoms in alkali metal clusters, the influence of temperature on structural and electronic properties is significant. The lowering of temperature reveals new spectroscopic features which are structure dependent. Optical response properties of small cationic Na+n clusters are characterized by rich molecularlike spectroscopic patterns, also with increasing size, and differ substantially from those found for neutral clusters. It has been clearly demonstrated that not only the number of valence electrons but its mutual interplay with the geometric properties determine optical response features. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470909
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  • 3
    Electronic Resource
    Electronic Resource
    Calculations of the structures, stabilities, Raman spectra, and NMR spectra of cadmium halide hydroxide (CdCln(OH2)a2-n, CdBrn(OH2)a2-n), and zinc chloride hydroxide (ZnCln(OH2)a2-n) species in aqueous solution (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 6494-6500 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100194a071
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  • 4
    Electronic Resource
    Electronic Resource
    Ab initio configuration interaction study of excited states of LiNa3 and Li2Na2 clusters: Interpretation of absorption spectra (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4934-4944 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ab initio configuration-interaction (CI) study of excited states of mixed alkali metal tetramers LiNa3 and Li2Na2 accounts for spectroscopic patterns obtained from the depletion spectra of neutral species, reproduces observed excitation energies and intensities for allowed transitions, and permits an assignment of cluster structures. For both mixed tetramers, the rhombic forms with a Li atom or atoms on the short diagonal are the most stable structures and give rise to predicted spectra in full agreement with the measured ones. The exact location of Li atoms seems to be more important in Li2Na2 than in LiNa3 since in the former case, only one isomer reproduces all features of the recorded spectrum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462736
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  • 5
    Electronic Resource
    Electronic Resource
    Quantum molecular interpretation of the absorption spectra of Na5, Na6, and Na7 clusters (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7938-7958 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The configuration-interaction study of the excited states of the most-stable structures of Na5, Na6, and Na7 clusters employing ab initio effective-core potential corrected by the core polarization potential predicts spectroscopic patterns which are in good agreement with the measured depletion spectra. A comparison of the transition energies and the oscillator strengths with the experimental data makes possible tentative structural assignments. Planar Na5 and Na6 structures and the three-dimensional pentagonal bipyramid for Na7 appear responsible for the recorded spectra. The full agreement between theory and experiment is present for Na6 and Na7. The measured cross sections and calculated oscillator strengths for Na5 compare better for lower transition energies than for higher ones. A many-electron description of the excited states of Na5, Na6, and Na7 yields a complete quantum molecular interpretation of the absorption spectra. From a comparison of the experimental and theoretical results the conclusion has been drawn that a transition from planarity to the three dimensionality takes place for Na7.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462346
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  • 6
    Electronic Resource
    Electronic Resource
    Ethyl 3-Hydroxybenzo[b]furan-2-carboxylate (1998)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 1951-1954 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108270198010336
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  • 7
    Electronic Resource
    Electronic Resource
    3-Methylthio-1,2,4-triazine: a Comparison of Experimental and Theoretical Structures (1998)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 550-553 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108270197016533
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  • 8
    Electronic Resource
    Electronic Resource
    Parallelism in computational chemistry (1993)
    Springer
    Theoretical chemistry accounts 84 (1993), S. 423-441 
    Details
    ISSN: 1432-2234
    Keywords: Computational chemistry application software ; Hypercube-connected multicomputers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An account is given of experience gained in implementing computational chemistry application software, including quantum chemistry and macromolecular refinement codes, on distributed memory parallel processors. In quantum chemistry we consider the coarse-grained implementation of Gaussian integral and derivative integral evaluation, the direct-SCF computation of an uncorrelated wavefunction, the 4-index transformation of two-electron integrals and the direct-CI calculation of correlated wavefunctions. In the refinement of macromolecular conformations, we describe domain decomposition techniques used in implementing general purpose molecular mechanics, molecular dynamics and free energy perturbation calculations. Attention is focused on performance figures obtained on the Intel iPSC/2 and iPSC/860 hypercubes, which are compared with those obtained on a Cray Y-MP/464 and Convex C-220 minisupercomputer. From this data we deduce the cost effectiveness of parallel processors in the field of computational chemistry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113280
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  • 9
    Electronic Resource
    Electronic Resource
    Parallel computational chemistry made easier: The development of NWChem (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 475-483 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe the design philosophy, structure, and supporting tool kits of the NWChem computational chemistry package. The primary purpose of this effort was to develop efficient parallel algorithms for a broad range of methods commonly used in computational chemistry. To facilitate this, we developed a shared nonuniform access memory model which simplifies parallel programming while at the same time providing for portability across both distributed- and shared-memory machines. In addition to this specific focus on parallelization, a substantial effort has been made to simplify the general problem of large-scale software development, which is common to many research groups. We find that this simplification can be achieved through judicious use of ideas from the computer science field of software engineering in the design and implementation of the program with minimal extra effort on the part of the chemist. © 1995 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560851
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  • 10
    Electronic Resource
    Electronic Resource
    Localized orbital calculations of the bonding in SO42-, SO2F2, ClO3F and SOCL2 (1972)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 6 (1972), S. 967-973 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Localized valence molecular orbitals have been obtained for SO42-, SO2F2, ClO3F and SOCl2 by the method due to Boys and Foster. The bonding in these molecules, in which the second row atom is exhibiting an excess valency, is discussed in terms of the form of these localized orbitals. The bonding of the second row atom to an oxygen atom is described by three bent bond orbitals, whilst bonding to a halogen atom is described by a single bond orbital. The participation of 3d functions in the various bonding and nonbonding orbitals is analysed in this localized orbital framework.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560060514
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