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  • 1990-1994  (478)
  • 1940-1944
  • 1993  (478)
  • Computational Chemistry and Molecular Modeling  (478)
  • 1
    Electronic Resource
    Electronic Resource
    Masthead (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993) 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480101
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  • 2
    Electronic Resource
    Electronic Resource
    Rayleigh-Schrödinger perturbation theory for nonlinear Schrödinger equations with linear perturbation (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 47 (1993), S. 469-483 
    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: Rayleigh-Schrödinger-type perturbation theory is developed for the nonlinear Schrödinger equation, which contains a linear perturbation operator. Typical applications involve the self-consistent reaction-field model of solvent effects. Consideration of external perturbations, like electric fields, allows. Calculation of the response properties of solvated species. The general formulae allow development of a consistent Møller-Plesset perturbation theory of solvated molecules. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560470606
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  • 3
    Electronic Resource
    Electronic Resource
    Electron correlation effects in the Rydberg-like 33D and 31D states of helium-like ions (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 1-14 
    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: The small and subtle effects of electron correlation in the Rydberg-like 31D and 33D states of the helium-like ions are studied using very accurate explicitly correlated wave functions. In particular, the effects of electron correlation on one-electron densities, probability distributions for the interelectronic distance, and their moments are examined with the help of density and Coulomb holes. Statistical electron correlation is examined with radial and angular correlation coefficients. The different methods of analysis provide complementary insight. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480102
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  • 4
    Electronic Resource
    Electronic Resource
    Ab initio study of the internal rotation barrier of formamide and the formamide-H2O complex (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 123-132 
    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: The barriers to internal rotation about the N—C bond of formamide and the formamide-H2O complex have been examined by ab initio quantum chemistry methods. Both self-consistent field and correlated approaches have been utilized to determine the geometries, energies, and local harmonic vibrational frequencies of the minimum-energy and transition-state structures of these two systems. We find that formamide's rotation barrier of 14-15 kcal/mol is increased to 16-18 kcal/mol when a single H2O molecule is attached. This result contrasts with the effect of a single H2O solvent molecule on the barrier to tautomerization of formamide (to form formamidic acid HN—CHOH) for which a barrier lowering of ca. 20 kcal/mol has been observed. The rotation barriers obtained for formamide and for its H2O complex are compared with barriers obtained experimentally in various solvents. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450202
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  • 5
    Electronic Resource
    Electronic Resource
    Some solutions in the graph theory of alternant benzenoids (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 167-176 
    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: A new formulation of the eigenvector equations for certain polymeric molecules is given. The electronic bands for the infinite molecules are deduced. For the finite molecules, the use of ghost molecules allows an exact specialization of the infinite to the finite eigenvector equations. The complete solution of the equations depends on the solution of a simple transcendental equation. Approximate solutions of this equation are given that bracket the accurate solutions so that, for molecules with many repeated moieties, the approximations become good. The general theory is illustrated by applications to the chrysene series and to the polyphenyls. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450204
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  • 6
    Electronic Resource
    Electronic Resource
    The fundamental syntopy of quasi-symmetric systems: Geometric criteria and the underlying syntopy of a nuclear configuration space (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 177-187 
    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: Point symmetry is a discrete concept; A nuclear configuration for a given stoichiometry either has or has not a particular point symmetry. By contrast, both static and dynamic properties of actual molecules exhibit continuous features. Using the formalism of fuzzy-set theory, we had previously proposed the concept of syntopy as a continuous extension of the symmetry concept for quasi-symmetric systems: This was based on an energetic criterion taking into account the energy costs of nuclear rearrangements. This extension of symmetry was necessarily dependent on the considered electronic state: For a given geometric arrangement of the nuclei, the energy cost of some rearrangement is dependent on the actual potential surface, that is, on the electronic state, in the Born-Oppenheimer approximation. In the extension of the syntopy model reported in the present work, we consider a syntopy criterion that is common to all electronic states. The syntopy thus defined - called the fundamental syntopy of the reduced nuclear configuration space - is independent of the potential surface and of the electronic state: It is defined only in terms of a geometric condition, which makes it more appropriate to rationalize mesoscopic structures. This new syntopy model provides a connection between all possible syntopies generated by the various potential-energy surfaces supported by the considered family of atomic nuclei. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450205
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  • 7
    Electronic Resource
    Electronic Resource
    Classical and quantum study of a generalized Kepler-Coulomb system (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 209-224 
    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: The nonrelativistic potential V = α/r + β cos θ/(r sin θ)2 + γ/(r sin θ)2, which constitutes an extension of the Kepler-Coulomb potential and of the Hartmann potential, is investigated from both a classical and a quantum mechanical viewpoint. The corresponding Schrödinger equation is solved in parabolic coordinates by using the Kustaanheimo-Stiefel transformation. The accidental degeneracy for the discrete spectrum is explained through the introduction of an su(2) dynamical invariance algebra. The Hamilton-Jacobi equation is solved in parabolic coordinates. The planarity and the periodicity of the trajectories are investigated. All finite trajectories are found to be quasi-periodic (rather than periodic as in the case of the Kepler-Coulomb system). © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450207
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  • 8
    Electronic Resource
    Electronic Resource
    Multiple time scale Hartree-Fock molecular dynamics (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 59-70 
    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: This is the first application of a rigorous, established multiple time-step method to ab initio molecular dynamics. The resulting algorithm is conceptually simple and easy to implement, but very effective. It translates the large mass differences present in ab initio molecular dynamics into substantial savings in computer time while retaining high accuracy. This transforms ab initio molecular dynamics from a desirable but prohibitively expensive possibility into a viable method, at least for short-time phenomena in small systems or for otherwise inaccessibly complicated potential energy surfaces. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450109
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  • 9
    Electronic Resource
    Electronic Resource
    Hylleraas-CI with linked correlation terms (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 87-95 
    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: Hylleraas-CI calculations with linked correlation terms of the form rpijrqkl are discussed. Formulas for the integration of the angular part are deduced and a method for the reduction of the radial part to auxiliary integrals is given. In the case of the Li atom, it is shown that for the calculation of the ground-state energy an ansatz for the wave function with at most two factors rpijrqkl is sufficient to achieve spectroscopic accuracy. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450111
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  • 10
    Electronic Resource
    Electronic Resource
    Recurrence relations for the evaluation of electron repulsion integrals over spherical Gaussian functions (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 257-265 
    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: Recurrence relations are derived for the evaluation of two-electron repulsion integrals (ERIs) over Hermite and spherical Gaussian functions. Through such relations, a generic ERI or ERI derivative may be reduced to “basic” integrals, i.e., true and auxiliary integrals involving only zero angular momentum functions. Extensive use is made of differential operators, in particular, of the spherical tensor gradient Ylm(∇). Spherical Gaussians, being nonseparable in the x, y, and z coordinates, were not included in previous formulations. The advantages of using spherical Gaussians instead of Cartesian or Hermite Gaussians are briefly discussed. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480407
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  • 11
    Electronic Resource
    Electronic Resource
    Atomic theorems (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 189-207 
    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: The atomic statement of the principle of stationary action determines the theorems that establish the mechanics of an atom in a molecule. The atomic torque, power, and current theorems are derived. They, along with the atomic force, virial, and continuity theorems, provide a complete description of the behavior of matter at the atomic level, including the effects of electric and magnetic fields. The atomic power theorem, for example, enables one to determine the atomic or molecular source of the creation and dissipation of power in combustion or in an explosion. An atom in a molecule is an open system and an atomic equation of motion for an observable contains a component corresponding to the flux in its current density through the atomic surface. The differential form of each theorem yields an equation of motion for the corresponding property density in which the same surface flux appears as a divergence of the current density. The differential and integrated atomic theorems complement those for the total system, enabling one to relate the property to its atomic components and ultimately to a local contribution from each element in real space. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450206
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  • 12
    Electronic Resource
    Electronic Resource
    Masthead (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993) 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450301
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  • 13
    Electronic Resource
    Electronic Resource
    On the applicability of a nonlinear Schrödinger equation to the determination of rate constants in Kramers' theory of chemical reactions (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 235-250 
    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: In 1940, Kramers derived an expression for the rate constant of chemical reactions in viscous media. In this theory, chemical reactions are modeled as Brownian processes in the presence of potential barriers. The derivation of the rate constant is based on the solution of the Smoluchowski equation, a Fokker-Planck-type equation in position space. Kramers' theory has been confirmed for reactions in systems ranging from nuclear processes to biochemical problems. The reaction rate can be obtained from the diffusion currents appearing in the Smoluchowski equation. A Smoluchowski-type equation in position space, similar to the one applied by Kramers, has been used to find a nonlinear Schrödinger equation (NLSE) for dissipative, frictionally damped systems, taking into account wave-particle duality. For several potentials, the NLSE can be solved exactly, and analytic expressions for the currents, appearing in the Smoluchowski equation and necessary to determine the rate constants, can be obtained. These currents are not only stationary, but can also be time-dependent. It will be shown that, essentially, the determination of the time-dependence of the currents can be reduced to the solution of Newton-type equations of motion. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450302
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  • 14
    Electronic Resource
    Electronic Resource
    Electronic states and nature of bonding in the molecule YN by all-electron ab initio CASSCF calculations (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 46 (1993), S. 145-157 
    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: In the present work, we present results of all-electron ab initio CASSCF calculations of nine electronic states of the molecule YN. Also reported are the spectroscopic constants derived on the basis of the calculated potential energies. The predicted electronic ground state is 1∑+, and this state is found to be separated from the excited states 3∑+, 3Π, and 1Π by 5177, 9290, and 9915 cm-1, respectively. The chemical bond in the YN molecule is polar with charge transfer from Y to N, giving rise to a dipole moment of 8.19 Debye at 3.3 au in the 1∑+ ground state is basically a double bond composed of two π bonds. The dissociation energy of the YN molecule has been derived as 4.59 eV. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560460115
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  • 15
    Electronic Resource
    Electronic Resource
    Masthead (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993) 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450401
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  • 16
    Electronic Resource
    Electronic Resource
    Nonlocal approximation to the exchange and kinetic energy functionals: Application to metallic clusters (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 333-347 
    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: The nonlocal weighted density approximation (WDA) to the exchange and kinetic energy functionals of many-electron systems proposed several years ago by Alonso and Girifalco in the context of density functional theory is used to compute, within the framework of the spherical jellium model, the ground-state electronic density, chemical potential, and total energy of neutral and negatively and positively charged sodium clusters containing up to N = 800 atoms. From these calculations, we study the behavior of the total energies per atom, chemical potentials, ionization potentials, I(N), and electron affinities, A(N). These results are compared with analogous calculations using the well-known Thomas-Fermi-Weizsäcker-Dirac (TFWD) approximation for the kinetic (TFW) and exchange (D) energy functionals. Calculations including the local density approximation (LDA) to the correlation energy in both WDA and TFWD functionals are also presented. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450402
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  • 17
    Electronic Resource
    Electronic Resource
    Coupling coefficients for systems with two open electronic shells: Transition metal ions with pM dN configuration (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 363-383 
    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 derived the necessary conditions to which the vector coupling coefficients (VCC) amn and bmn, describing atomic L, S-multiplets of pMdN and dNs1 configurations (1 ≤ N ≤ 9, 1 ≤ M ≤ 5), should satisfy. It is shown that for two-open-shell systems under consideration the unknown VCC should satisfy not only usual restrictions resulting from the spheric symmetry, but also some additional equation introduced in the present paper in the form of a postulate. VCC obtained were used for the ab initio calculations (by the general SCF coupling operator method) of several transitionmetal atoms and ions with electronic configurations 3d14p1, 3p43d3, and 3p53d3. To check the presented theory, we carried out a detailed comparison between these results and analogous data, obtained by the atomic Roothaan-Hartree-Fock method [2]. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450404
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  • 18
    Electronic Resource
    Electronic Resource
    Solution of atomic and molecular Schrödinger equation described by hyperspherical coordinates (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 385-390 
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    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: The Schrödinger equation for an atom or molecule is expressed in terms of hyperspherical coordinates. The eigenfunction is expanded in a series of orthonormal complete sets: Yλ,μ(Ω), eigenfunctions of generalized angular momentum scalar operator, and Lvn, generalized Laguerre polynomials. The recurrence relation of the expansion coefficients are derived and the eigenvalues can be obtained from the secular equation. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450405
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  • 19
    Electronic Resource
    Electronic Resource
    Unrestricted Hartree-Fock method for infinite systems with antiferromagnetic array: Analysis of antiferromagnetic state of trans-polyacetylene (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 391-400 
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    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: An improved unrestricted Hartree-Fock (UHF) crystal orbital method for infinite one-dimensional systems having antiferromagnetic spin array is presented. This variational version of the UHF method is composed of two steps of self-consistent-field (SCF) calculations. The second SCF equation is to be solved using the canonical transformation between specific crystal orbitals around the Fermi level of the first conventional SCF solution. The energy gain and the forbidden band gap (correlation gap) associated with the hypothetical antiferromagnetic state of trans-polyacetylene are examined as an example. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450406
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  • 20
    Electronic Resource
    Electronic Resource
    Applied many-body methods in spectroscopy and electronic structure. Edited by D. Mukherjee, Plenum Publishing Co., New York and London, 1992 (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 401-401 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450407
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  • 21
    Electronic Resource
    Electronic Resource
    Dipole, quadrupole, octupole, and dipole-octupole polarizabilities at real and imaginary frequencies for H, HE, and H2 and the dispersion-energy coefficients for interactions between them (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 349-361 
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    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 have calculated certain dynamic polarizabilities (for both real and imaginary frequencies) for H, He, and H2 and the dispersion-energy coefficients for long-range interactions between them. We have done so in a sum-over-states formalism with explicitly electron-correlated wave functions to describe the states. To be precise, we have determined the dipole (α1), quadrupole (α2), and octupole (α3) polarizabilities of H and He for real frequencies (ω) in a range between zero and the first electronic-transition frequency and for imaginary frequencies (iω) on a 32-point Gauss-Legendre grid running from zero to ħω = 20 Eh, and for H2, we have found the dipole (α), quadrupole (C), and dipole-octupole (E) polarizability tensors for the same real and imaginary frequencies. The dispersion-energy coefficients, obtained by combining the sum-over-states for-malism for the polarizabilities with analytic integration over ω, gave values of C6, C8, and C10 for the atom-atom systems; C06, C26, C08, C28, and C48 for the atom-diatom systems; and C6, C′6 and C″6 for the H2—H2 system. Nearly all the results are considered to be more reliable than those hitherto published and some have been obtained for the first time, e.g., C(iω), E(ω), and E(iω) for H2 and C08, C48, and C48 for the H—H2 system. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450403
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  • 22
    Electronic Resource
    Electronic Resource
    Theoretical and computational models for organic chemistry. Edited by S. J. Formosinho, I.G. Csizmadia, and L.G. Arnaut, Nato Asi Series C, vol. 339, Kluwer, Dordrecht, 1991 (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 403-403 
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    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450408
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  • 23
    Electronic Resource
    Electronic Resource
    Masthead (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993) 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450501
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  • 24
    Electronic Resource
    Electronic Resource
    Atomic integrals containing r23λr13μr12ν with λ, μ, ν ≥ -2 (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 445-470 
    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: In this paper, the efficient evaluation of the atomic integrals I =∫r1ar2br3cr23λr13μr12νe-αr1-βr2-γr3dτ with one or two factors rij-2 is described. These integrals are necessary for a lower-bound calculation for Li-like systems using the method of variance minimization or Temple's formula. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450504
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  • 25
    Electronic Resource
    Electronic Resource
    Møller-Plesset expansion of the dispersion energy in the ring approximation (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 409-431 
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    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: Coupled-cluster equations for the calculation of the nonexpanded (fully damped) dispersion energy are derived. These equations are solved in the ring approximation using the Møller-Plesset expansion in terms of the fluctuation potentials WA and WB for the individual molecules. Numerical results of high-order perturbative calculations for the He, H2, LiH, H2O, and HF dimers are presented and compared with the converged results computed using the same basis sets. It is found that the convergence of the Møller-Plesset expansion of the dispersion energy in the ring approximation is very fast. The padé approximants still accelerate this already good convergence. For all complexes studied in this paper, the sum of the corrections through the second-order in WA + WB reproduces over 99% of the converged value. The sum of third- and higher-order corrections in the ring approximation is found to be one or two orders of magnitude smaller than the sum of second-order terms not included in the ring approximation and, therefore, may be safely neglected. Thus, it appears that a second-order calculation, which does not require iterating coupled-cluster equations or solving random phase approximation equations, offers the best compromise between accuracy and computational requirements. © 1993 John Wiley & Sons, Inc.
    Additional Material: 12 Tab.
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    General algebraic expressions of totally symmetric potential functions for AXn (n = 3,4) molecules (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 471-484 
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    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: The integrity bases for representations of the nuclear permutation groups Sn (n = 3,4) in the space of internal coordinates describing AXn molecules are determined. This allows optimal expressions of the molecular potential energy functions in terms of internal coordinates that are totally symmetric with respect to permutations of indistinguishable nuclei. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560450505
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    Electronic Resource
    Masthead (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993) 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450601
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    List of participants (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 491-505 
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    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450603
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    Introduction (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 489-490 
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    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450602
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    A theoretical study of the effect of basis sets on stationary structures for the addition of carbon dioxide to methylamine: A relation among geometries, energy status, and electronic structures (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 433-444 
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    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: The carbon dioxide (CO2) to methylamine (CH3NH2) addition reaction is investigated using an ab initio MO method with the aim of obtaining an insight into the relation between transition-state structure and reactivity. The complete potential energy hypersurface was explored and the stationary points representing reactants, transition state, and product were localized. To establish the relevance of different basis sets, calculations were carried out at different levels of theory: STO-3G, 3-21G, 4-21G, 4-31G, 6-31G, 6-311G, 6-31G*, and MP2/6-31G*//HF/6-31G*. A reaction analysis done by correlation of bond-order indices using the More O'Ferrall-Jencks diagram reveals the reaction mechanism as an asynchronous process. The transition state can be described as a four-membered ring. The lone nitrogen electron pair of the amine appears as the driving force of the reaction, where a positive hydrogen rather than a radical is more likely to be transferred. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560450503
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    Enrico clementi: Gradus ad parnassum (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 507-510 
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    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450604
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    Some applications of nonlinear convergence accelerators (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 545-562 
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    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: A number of established nonlinear convergence acceleration methods are presented. It is discussed how these methods, and also some new algorithms, can be applied successfully to Fourier series. Some of the new accelerators are tailored for these-series. Others are also useful for other types of series and sequences, and not only for convergence acceleration, but also for extrapolation or summation problems. Applications to the numerical inversion of the Laplace transform and to a Fourier series arising in the Matsubara formalism are presented. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560450606
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    Time scales and other problems in linking simulations of simple chemical systems to more complex ones (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 511-544 
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    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 shall start with very small systems like H2 and H3, computed with very accurate methods (Hylleraas-CI) or atomic systems up to Zn with accurate methods (CI), then move to more complex ones, like C60, but now with somewhat less accurate methods, specifically Hartree-Fock with density functionals, the latter for the correlation energy but not for the exchange energy. For even more complex tasks like geometry optimization of C60, we have resorted to even simpler and parametrized methods, like local density functionals. Then, we could use quantum mechanics either to provide interaction potentials for classical molecular dynamics or to directly solve dynamical systems, in a quantum molecular dynamics approximation. Having demonstrated that we can use the computational output from small systems as input to larger ones, we discuss in detail a new model for liquid water, which is borne out entirely from ab initio methods and nicely links spectroscopic, thermodynamics, and other physicochemical data. Concerning time scales, we use classical molecular dynamics to determine friction coefficients, and with these we perform stochastic dynamic simulations. The use of simulation results from smaller systems to provide inputs for larger system simulations is the “global simulation” approach, which, today, with the easily available computers, is becoming more and more feasible. Projections on simulations in the 1996-1998 period are discussed, new computational areas are outlined, and a N4 complexity algorithm is compared to density functional approaches. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    Accurate second-order correlation energies for Mg and Ar (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 563-572 
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    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: A p-version finite element method has been used to calculate second-order pair and total correlation energies for closed-shell Mg and Ar. Comparison with the best results found in the literature suggests that the present values are the most accurate and that the method should perform comparatively better for heavier elements. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Tab.
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    4-Currents in relativistic quantum chemistryIt is a pleasure to dedicate this paper to Professor Enrico Clementi, whose energy, initiative, and technical brilliance have contributed so much to the development of quantum science. Among the astonishing range of fields to which Professor Clementi has made important contributions is relativistic quantum chemistry, and we are happy to be able to discuss one aspect of this field in the present paper. (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 573-585 
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    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: Some topics in relativistic quantum chemistry are reviewed with special emphasis on 4-currents and 4-potentials. It is shown that, both in molecular quantum theory and in solid-state physics, calculations can include relativistic and magnetic effects by means of 4-currents without an excessive increase in complication, provided that 4-component Dirac spinors are used rather than the Pauli approximation. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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    Electronic stopping power for protons in an LiF monolayer (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 219-226 
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    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: In our previous work, the stopping properties of metallic and covalent films were investigated. Here we consider an ionically bound film. The energy loss of a proton in an LiF monolayer (LiF-1L) is calculated in orbital fashion, based on kinetic theory. The required momentum density and mean excitation energy are obtained from the local density approximation and local plasma approximation respectively. For comparison, the LiF molecule is treated by use of a large intermolecular distance in the film. We find the stopping cross section of the LiF molecule to be only slightly larger than that for the LiF-1L. The Bragg rule (additivity of stopping for the corresponding atoms) is not valid for the ionically bound molecule nor the corresponding extended system, but may be valid if additivity of stopping of atomic ions is assumed. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480824
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    Energetics of small clusters of stabilized jellium: Continuum and shell-structure effects (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 249-261 
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    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 evaluate binding energies, ionization energies, and second-order energy differences as functions of valence electron number for small spherical clusters of stabilized jellium, using the Kohn-Sham equations with the local-spin-density (LSD) approximation. Cohesive energies are also reported. A comparison is made with semiclassical formulas (liquid drop model and Padé approximant, with surface and curvature coefficients derived from first principles). These formulas nicely average the shell-structure oscillations of the energy, which are found to be almost the same as for ordinary jellium. Spherical clusters with 1, 7, and 9 electrons have binding energies very close to those of the semiclassical predictions. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480827
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    Multiconfigurational spin-adapted single-reference coupled cluster formalism (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 269-285 
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    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 exploit the unitary group formalism in formulating a multiconfigurational single-reference coupled cluster method for cases involving one or two electrons in open shells. The linear version of CCSD theory for the simple open shell case and for low lying singlet states of closed shell systems are considered in detail. The entire formalism is related to the unitary group based CISD method, and explicit expressions for size-extensivity corrections, leading to the L-CCSD formalism, are given. An illustrative example of the minimum basis set model of the BeH radical is also presented. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480829
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    A note on the calculation of some transformation coefficients (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 303-308 
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    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: This article gives an improved derivation for U(n1 + n2) ⊃ U(n1) × U(n2), SN1+N2 ⊃ SN1 × SN2, and other transformation coefficients by using a series of elementary Racah transformations. These transformation coefficients can be expressed generally in terms of a product of segments containing 6j symbols and easily calculated. Possible segment factors are given in Table I. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480831
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    Variation-iteration method in momentum space: Determination of Hartree-Fock atomic orbitals (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 609-618 
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    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: A method using the Svartholm iterative procedure to solve atomic Hartree-Fock equations in momentum space is defined and applied to the ground states of Be and B+. The calculated atomic orbital properties follow a monotonic and stable convergence, but with rates of convergence depending on each property. The evolution of the orbitals during the iterations is explained by the combined actions of the variational principle, the Svartholm iterative procedure, and the momentum space representation. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450611
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    Resolution of Schrödinger's equation for a scattering problem by a finite-element method (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 637-647 
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    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 present a new numerical method for solving the Schrödinger equation in the case of scattering or tunneling states. As an example, we study a model of the scanning tunneling microscope. The method uses a finite-element approximation of the wave function in the region of the scattering potential. From the wave function that we obtain, we derive the tunnel current density. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560450613
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    Kinetic energy component in the divide-and-conquer method (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 355-361 
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    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: The kinetic energy component is shown to be a well-defined quantity in the divide-and-conquer method. This kinetic energy converges to the conventional Kohn-Sham kinetic energy when the numbers of the “buffer atoms” for subsystems increase. Numerical results from sample calculations confirm that the kinetic energy component converges to the Kohn-Sham value as the basis set increases. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480836
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    Determinantal inequalities among 〈rn〉 (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 377-384 
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    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: This paper considers two types of 2 × 2, 3 × 3, and 4 × 4 determinantal inequalities. The elements of one type are 〈rn〉, while the elements of the other type are c〈rn〉;, where c = 3 + n. The 2 × 2, 3 × 3, and 4 × 4 determinantal inequalities involve n = -1, 0, 1, n = -1, 0, 2, 3, 4, and n = -1, 0, 1, 2, 3, 4, 5. The two types of 2 × 2, 3 × 3, and 4 × 4 inequalities are used to obtain lower bound estimates of 〈r〉, 〈r3〉, and 〈r5〉 for the noble gas atoms He, Ne, Ar, Kr, and Xe. The values of these quantities obtained from the inequalities are compared with the quantum mechanical values of Boyd, who calculated them with the near Hartree-Fock analytical wave functions of Clementi and Roetti. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560480838
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    Relativistic quantum defect orbital calculations of singlet-singlet transitions in the zinc and cadmium isoelectronic sequences (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 385-397 
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    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: Relativistic quantum defect orbital (RQDO) calculations, with and without explicit account for corevalence correlation, have been performed on several electron transitions in the zinc and cadmium isoelectronic sequences, which are of interest in astrophysics and fusion plasma research. A comparative study with other theoretical results and experimental measurements has also been carried out. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480839
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    Electric multipole moment integrals evaluated over slater-type orbitals (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 431-450 
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    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 study integrals that arise in the calculation of electric multipole moments. A computational approach is developed to evaluate these integrals in an STO basis set in a straightforward, yet somewhat untraditional fashion. The computation involves a simple three-step procedure: translation of all Cartesian parts to one center, local evaluation, and a single one-sided rotation into the molecular frame. Some assessment on this method is discussed. An implementation of the method is presented in this paper to compute overlap, dipole, quadrupole, octopole, and hexadecapole moment integrals in a basis set that includes up to g orbitals. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480843
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    Theoretical study of ionization potentials in monosubstituted benzenes (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 46 (1993), S. 651-669 
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    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: Monosubstituted benzenes, in which the substituents participate in the π-electron system, are studied following a classification in two classes according to the π-electronic structure of the substituent. For this type of molecule, a relation is established between the nature of the substituent and, on the one hand, the energies of the two highest occupied molecular orbitals and, on the other hand, their respective differences. The two orbitals referred to above have π-character and belong to the a2 and b1 species if a C2v point group is assumed. Simple symmetry arguments lead to the conclusion that the a2 orbitals have, essentially, an intraring character, whereas the π-orbitals of the substituents do give an important contribution to the b1 orbitals. Therefore, an a2 electron must have a larger interaction with the benzene ring and a smaller kinetic energy, whereas a b1 electron must have a larger interaction with the substituent and a larger kinetic energy. It is also expected that the changes in the π-electronic structure of the substituent must much more influence the variations on the b1 energies and on the components of orbital energies associated with the substituent than the variations on the a2 energies and on the intraring components of the orbital energies. A modified version of the MOPAC program was prepared to perform the decomposition of the orbital energies in their kinetic and potential energy components and these in their monocentric and bicentric terms. MNDO calculations on nine monosubstituted benzenes, using the modified MOPAC program, give good confirmation of the symmetry predictions and prove the consistency of the classification of the substituents that is introduced. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560460506
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  • 47
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    Proton transfer to ubiquinone QB in the photosynthetic reaction center of Rps. Viridis: The role of electrostatic interactions (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 89-106 
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    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: Electrostatic calculations of the pKa of ionizable groups in the reaction center of Rhodopseudomonas (Rps.) viridis were carried out to investigate three possible mechanisms for proton transfer to the singly reduced acceptor ubiquinone QB. The program DelPhi, which solves the Poisson-Boltzmann equation given the distribution of charges and dielectric boundaries, was used to determine the electrostatic potential. The shift in pKa of the titratable residues in the QB binding pocket in response to the one-electron reduction and following protonation of QB was obtained from calculated interactions with the reaction field, background protein dipoles, charged cofactors, and other ionizable residues. A limited number of bound waters was also included in the computations as titrating sites. Their titration behavior was shown to be strongly coupled to neighboring ionizable sites. The results show that strong electrostatic interaction between the radical anion QB-· and a neighboring serine residue (SER L 223) as well as the protein environment stabilize a system in which the incoming proton is localized on serine and only shared in a hydrogen-bonding relationship with QB-·. These results hint to the possibility that actual proton transfer to QB-· only occurs after a second negative charge has been added to the system through transfer of a second electron either to the menaquinone QA, with formation of the QB-· QA-· system, or to QB-·, leading to the doubly reduced QB2-. This preposition is consistent with spectroscopical and electron nuclear double resonance (ENDOR) experimental results for bacterial reaction centers (RCs) failing to find evidence for the existence of the protonated semiquinone QBH·. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480712
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    Behavior of interaction energy and intramolecular bond stretch in linear and bifurcated hydrogen bonds (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 181-190 
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    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: It is first demonstrated that a simple Morse potential can fit very well the ab initio interaction energy for both the linear H bond of the water dimer and the bifurcated arrangement in HOH‥HOCHCHOH, using simple physical properties as the parameters in the function. This energy correlates linearly with the stretching observed in the internal OH bond of the proton donor water, leading to the formulation of an analogous Morse function that can describe the latter stretch. Although simple physical parameters can be used for the linear H bond, a good fit is achieved in the bifurcated case only after the parameters are adjusted empirically. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480719
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  • 49
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    Electronic Resource
    Introduction (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. ix 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480802
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  • 50
    Electronic Resource
    Electronic Resource
    Counterion condensation theory revisited: Limits on its applicability (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 213-230 
    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: Metropolis Monte Carlo and Poisson-Boltzmann calculations were done to quantitatively assess the conditions under which counterion condensation (CC) theory could be considered valid. The fundamental prediction of condensation theory, that the number of counterions bound to a polyelectrolyte molecule can be predicted by a single parameter describing the linear charge density of the charged system, was shown to be quantitatively correct for a range of conditions. To define the number of counterions bound, it was necessary to use an energy-based criterion by which ions that interact with the polyion with an energy less than -kT were considered bound. Using this criterion, Monte Carlo calculations on systems consisting of charged cylinders and a neutralizing number of counterions in a dielectric continuum showed that the number of bound counterions was quantitatively predictable by the CC relation (1-1/ξ) for systems with a linear charge density and dimensions approaching those of duplex or triplex DNA. Poisson-Boltzmann (PB) calculations on cylinders with different linear charge densities and radii have been done to assess the limits of the CC prediction that the number of counterions bound is a constant even as the bulk concentration of electrolyte in the surrounding is increased. As in the case of the MC calculations, the validity of the CC prediction is seen to increase with increasing linear charge density of the charged cylinder. The agreement between PB and CC is seen to be very good for highly charged cylinders. The results described here provide justification for the use of CC theory for interpreting experimental data on polyelectrolytes of the approximate dimensions and linear charge density of duplex or triplex DNA. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480722
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  • 51
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    The diatomic molecule project at LMSS 1956-1966: Broken bottlenecks (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 25-32 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480806
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  • 52
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    Electronic Resource
    On the solid state of hydrogen fluoride: A self-consistent crystal field study (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 46 (1993), S. 109-118 
    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: A recently developed self-consistent crystal field (SCCF) method is applied to two suggested crystal structures of solid hydrogen fluoride, polar and nonpolar, respectively. Constrained geometry optimizations are performed and the results are compared with experiment and previous theoretical studies. Comparisons are also made with a previous SCCF study on hydrogen cyanide. The Pauli repulsion, dispersion, and “classical” crystal field contributions to the lattice energy are calculated. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560460111
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  • 53
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    Electronic Resource
    Ab initio investigation of void stabilization: Oxygen in Nickel (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 163-173 
    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 have used the ab initio technique of UHF/LANL 1 MB to study the interactions between absorbed oxygen atoms and molecules with their host nickel lattice. The host lattice is approximated by a small cluster of nickel atoms that are arranged as face-centered-cubic, except for a tubular void described by the absence of three or four lattice elements. The oxygen absorbates are placed, one at time, within this cavity. We conclude that, for tubular cavities, the interaction between the nickel lattice and the oxygen absorbates is stronger than the interactions between pairs of oxygen atoms, suggesting that the absorbates are mostly atomic (as apposed to diatomic) in character, while the (energetically) most preferred number of oxygen atoms to reside inside an n-site, tubular hollow of nickel is simply (n - 1). © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480819
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  • 54
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    Electronic Resource
    V4+ doping into SiO2, ZrO2 and ZrSiO4 structures. An ab initio perturbed ion study (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 175-186 
    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: An ab initio perturbed ion study using X-ray diffraction data has been carried out for ZrSiO4 (zircon), ZrO2 (monoclinic zirconia, baddeleyite), and SiO2 (α-cristobalite) crystal lattice structures. The different substitutions of V4+ for Zr4+ and Si4+ occurring in these host lattices have been analyzed. Geometry optimizations have been performed with the aim of determining the relative stability, cell parameters, and force constants of radial displacement associated with the local relaxation for pure and doped structures. Numerical results are confronted against experimental data and compared with previous results. The geometrical cell parameters of different structures obtained by computer simulation and the results of the X-ray diffraction studies agree with previous experimental data. For the zircon lattice, the substitution of V4+ for Zr4+ at an eightfold-coordinated site is energetically favorable while the substitution of V4+ for Si4+ at a fourfold-coordinated site is unstable. For ZrO2, the substitution of V4+ for Zr4+ is energetically favorable while the substitution of V4+ for Si4+ in SiO2 is energetically unfavorable. There is less sensitive influence of the crystal lattice parameters for substitutions occurring at the eightfold-coordinated ion site in ZrSiO4 and SiO2 structures. The doping process produces a decrease of force constant (k) values associated with the breathing fundamental vibrational mode for all structures. The k associated with the radial displacement in dodecahedral substitution in the ZrSiO4 structure is especially high. The force constants for this movement in tetrahedral substitution in the ZrSiO4, ZrO2, and SiO2 structures have a lower value. The differences between ionic radii reported by Shannon and Prewitt of the species concerned in the doping process are not capable of explaining the relaxation of crystal lattice parameters in the ZrO2 and SiO2 structures. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480820
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  • 55
    Electronic Resource
    Electronic Resource
    Some density-functional LMTO studies of electronic properties of quasi-one-dimensional systems (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 227-243 
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    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: Results of first-principles, density-functional, LMTO calculations on quasi-one-dimensional systems are presented. Special emphasis is put on the problems related with studying the properties of real materials by means of electronic structure calculations. As examples we discuss undoped and doped trans polyacetylene, an MX chain compound, CaNiN, and a comparison between polycarbonitrile and hydrogen cyanide. It is argued that single-chain calculations on undoped polyacetylene predict a bond-length alternation, whereas this may be suppressed in multichain calculations. For an MX chain we demonstrate the importance of including the full ligand structure, whereas many properties of CaNiN can be understood as intrinsic to single chains. A comparison between the covalently bonded polycarbonitrile and the hydrogen-bonded hydrogen cyanide reveals differences between delocalized and localized electrons but also inaccuracies in the relative total energies. Finally, results for doped trans polyacetylene indicate relatively large electronic dopant-polymer hopping integrals as well as problems in describing electron transfers for weakly interacting systems when using a local-density approximation. In total it is demonstrated that reliable and useful informations are obtained in most cases, but also that one has to be careful in choosing the idealized system that is to represent the real material and that certain aspects of the local-density approximation should be improved. © 1993 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480825
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  • 56
    Electronic Resource
    Electronic Resource
    Related upper and lower bounds to atomic binding energies (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 46 (1993), S. 675-688 
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    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: The method proposed by Singh for the calculations of lower bounds to atomic binding energies has been generalized to encompass upper bounds as well. The result is a pair of related matrix eigenvalue problems, constructed from similar sets of basic matrix elements, with the solution of one yielding the tower bound, and of the other, the upper bound. The upper bounds are identical to those calculated by the Rayleigh-Ritz method, which can be useful when the inversion of the normalization matrix is ill-conditioned. The lower bounds are comparable with the best available in the literature. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560460602
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  • 57
    Electronic Resource
    Electronic Resource
    Molecular SCF calculations using a basis of numerical orbitals (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 321-330 
    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: Techniques for computing the multicenter integrals required for molecular calculations for orbitals for which the radial factors are given numerically are described. The methods make extensive use of a numerical algorithm for computing spherical Bessel transforms. The feasibility of using these methods is demonstrated by applying them to SCF calculations for the methane molecule. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560480833
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  • 58
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    Electronic Resource
    Success and pitfalls of the dielectric continuum model in quantum chemical calculations (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 451-466 
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    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: Recently we presented an extension of the direct reaction field (DRF) method, in which a quantum system and a set of point charges and interacting polarizabilities are embedded in a continuum that is characterized by a dielectric constant ∊ and a finite ionic strength. The reaction field of the continuum is found by solving the (linearized) Poisson-Boltzmann equation by a boundary element method for the complete charge distribution in a cavity of arbitrary size and form. Like many other authors, we found that the results depend critically on the choice of the size of the cavity, in the sense that the continuum contribution to the solvation energy decreases rapidly with the relative cavity size. The literature gives no clues for the definition of the cavity size beyond “physical intuition” or implicit fitting to experimental or otherwise desired results. From theoretical considerations, a number of limitations on the position of the boundary are derived. With a boundary defined within these limitations, the experimental hydration energies cannot be reproduced, mainly because of the neglected specific interactions. In addition, we found that the description of the solute's electronic states also depends on the solvation model. We suggest that one or more explicit solvent layers are needed to obtain reliable solvation and excitation energies. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480844
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  • 59
    Electronic Resource
    Electronic Resource
    Solvent effect on the potential surface of the proton transfer in [H3N—H—NH3]+ (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 491-499 
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    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: Statistical mechanics Monte Carlo simulations of the proton transfer in [H3N—H—NH3]+ in aqueous solution have been carried out using the combined quantum mechanical and molecular mechanical AM1/TIP3P potential. As in the gas phase, squeezing and stretching motions of the donor-acceptor distance have profound effects on the proton transfer. Solvation increases the activation free energy of the proton transfer by 3 kcal/mol over that in the gas phase. The results suggest that the combined QM/MM potential may be used in models that treat the proton motion quantum mechanically and the solvent dynamics classically. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480847
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  • 60
    Electronic Resource
    Electronic Resource
    Assessment of molecular shape fluctuations along dynamic trajectories (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 547-566 
    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: To assess the flexibility of a molecule (and to establish how it is affected by external conditions), one can analyze the nature of the configurations encountered along molecular dynamics (MD) trajectories. If the molecule is initially at a rigid conformation, then it will mostly undergo deformations which conserve the initial fold or shape. That is, a rigid molecule will exhibit very small shape fluctuations about the initial shape, whereas large fluctuations will be characteristic of flexible molecules. Establishing the persistence of molecular shape features along MD trajectories is a valuable piece of information in the analysis of dynamic phase transitions in large biomolecules, including protein folding and polymer melting. In this work, we discuss a methodology to monitor macromolecular shape along dynamic trajectories. The procedure uses descriptors which convey some global shape features, including the compactness and degree (and complexity) of entanglement in a backbone. The method is used to follow shape fluctuations in chain molecules (carboxylic acids) and cyclic molecules (cycloalkanes), with 6 up to 12 carbon atoms. The role of variable temperature and number of atoms on these fluctuations is analyzed. The results indicate a relatively constant average shape in the cyclic molecules, although the amplitude of the shape fluctuations increases with the temperature. In contrast, the shape of the chain molecules is affected largely at high temperature, where folding or “melting” becomes dominant. At low temperature, the chains are very rigid. In the high temperature regime, the shape fluctuations in chains are large and very similar to those in cycles. In other words, the distinction between configurations of cycles and chains starts to blur at high temperature, thus suggesting that chains are mostly folded into turns. The results would appear not to depend very strongly on the functional group at the end of the chain. © 1993 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480851
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  • 61
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    Theoretical study of the reaction of Cd(1S, 3P, 1P) with the methane molecule (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 587-598 
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    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: The reaction pathways of the interaction of the methane molecule with the cadmium atom in the ground state (1S) and the two lowest excited states (3P, 1P) were determined using Hartree-Fock followed by multireference configuration interaction plus second-order multireference Möller-Plesset calculations. No spontaneous activation of the methane molecule was observed by these electronic states of the cadmium atom due to the existence of activation barriers of 107.2, 27, and 17.3 kcal/mol, respectively. The geometry and electronic structure of the HCdCH3 intermediate molecule and the CdH and CdCH3 products involved in the reaction were also determined, as well as the dissociation pathway of HCdCH3 towards the CdH + CH3 and H + CdCH3 products. We found that the HCdCH3 intermediate reaches the final products without any barriers and also that the initial reactants in the ground state need to be provided with 88.5 kcal/mol to obtain the CdH + CH3 products and with 99.8 kcal/mol to get the H + CdCH3 products. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480853
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  • 62
    Electronic Resource
    Electronic Resource
    Light particles interacting with organic molecules (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 607-620 
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    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: Slow electron scattering from CH4, and thermal positrons annihilating with a variety of organic molecules, will first be discussed, the major role of molecular polarizability being the focal point. In the same context, initially neutral carbon clusters with an added, but now bound, electron will be considered, and in particular for C60- the role of polarizability will again be stressed. Some attention will also be paid to electron-electron interaction in C60- -. Photoelectron spectroscopic data on ionization potentials for both linear and terminated polyacenes will then be briefly considered, both the role of hole localization and hole-hole interaction being referred to in these quasi-two-dimensional systems. Finally some directions for further work are proposed. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480855
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  • 63
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    Electronic Resource
    Partial widths of feshbach funnel resonances in the Na(3p) · H2 exciplex (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 621-632 
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    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 have located five zero-angular-momentum resonance states in the funnel associated with the lowest conical intersection of the Na (3p) · H2 exciplex, and we have characterized the four narrowest of these in terms of total and partial widths. The resonant contributions of the metastable states to state-to-state energy transfer greatly exceed the background contributions. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480856
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  • 64
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    A mutually consistent procedure for excitation energies and transition densities based on the extended Brillouin's theorem (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 47 (1993), S. 155-173 
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    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: A mutually consistent method to calculate excitation energies and corresponding transition densities is proposed. The method is based on the extended Brillouin's theorem that is derived from the nonstationary variation principle. Within the proposed procedure, the Brillouin's conditions, which appear in this extension, are used as a set of nonlinear equations for molecular orbitals and configuration interaction coefficients of the trial ground- and excited-state functions. The excitation energy is an eigenvalue of the set. To some extent, this procedure is related to the variational treatment of the conventional random-phase approximation within the equation-of-motion method. The basic features of the proposed procedure are discussed and it is illustrated by numerical examples. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560470207
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  • 65
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    Decay dynamics of a metastable state in a time-varying electric field: A three-level prototypical system (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 47 (1993), S. 213-223 
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    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: In a numerical experiment, the dynamics of natural decay of a metastable state is shown to be strongly affected by the presence of an external time-varying electric field of high intensity. The metastable state, depending upon its level width, is shown to be stabilized by a near-resonant electric field. The applied field may even cause population transfer to a neighboring bound level that is not directly populated by the natural decay process. The effects of continuous and pulsed perturbations are both analyzed numerically, and perturbation, theoretically. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560470305
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  • 66
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    Helical region of the potential energy surface of α-aminoisobutyric acid: A theoretical study (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 47 (1993), S. 231-238 
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    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: The helical region of the potential energy surface of blocked α-aminoisobutyric acid (Aib) dipeptide has been studied by using ab initio and semiempirical quantum mechanical methods, as well as force-field-derived methods. Depending on the method, an α-helix or a 310-helix is found to be the energy minimum. The conformations obtained from computations performed at the ab initio quantum mechanical level, as well as by using the AMBER force field, are in excellent agreement with X-ray data. Semiempirical results display some important differences with regard to experimental data. On the other hand, the CVFF force field predicts no energy minimum in the helical region of the Aib potential energy surface. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560470307
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  • 67
    Electronic Resource
    Electronic Resource
    Valence electronic states of NH2+ and PH2+ dications (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 355-365 
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    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: The ab initio second-order effective valence-shell Hamiltonian that is based on the multireference many-body perturbation theory has been applied to determine adiabatic potential energy curves for the valence states of NH2+ and PH2+ dications. For PH2+, three low-lying quasi-bound states (X1∑+, a3 Π, A1Π) are found and their spectroscopic constants are characterized. In NH2+, no quasi-bound states are found. The potential energy curves for NH2+ are compared with those for PH2+ to understand the difference between these two valence isoelectronic cations. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480603
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  • 68
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    Announcement (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 385-385 
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    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480606
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    Some comments on the counterpoise correction for the basis set superposition error at the correlated level (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 375-384 
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    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: The use of the counterpoise method for the mitigation of basis set superposition error at the correlated level is discussed. Evidence is presented to show that the ghost basis plays a dual role in the counterpoise method: The orbitals of the system are improved by the ghost basis but at the expense of a nonphysical increase in the dimension of the virtual space. This second factor has no effect on application of the counterpoise method at the SCF level but it makes the use of the counterpoise method at the correlated level much less straightforward. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480605
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  • 70
    Electronic Resource
    Electronic Resource
    Introduction (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. v 
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    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480702
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    Hydroxyl stretching in substituted phenols: An AM1 study (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 7-15 
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    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: Hydroxyl-stretching frequencies (vOH) were estimated for a number of 4-substituted and 2,6-disubstituted phenols using the AM1 all-valence electron molecular orbital approximation. There was significant correlation between calculated and experimentally observed frequencies with better correlation observed with the gas phase as compared with dilute solution-phase values. Significant Hammett sigma-rho relationships were recorded for the 4-substituted phenols, consistent with experimental observations. The vOH stretching frequency associated with the equilibrium structure of 2,6-di-t-butylphenol was calculated to be 15 cm-1 higher than that of phenol and this increase was attributed to steric interactions that act to effectively shorten the OH bond length. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480705
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    1993 Saniebel symposia list of participants (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. vii 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480703
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    Local density and gradient-corrected functionals for short-range correlation: Antiparallel-spin and non-RPA contributions (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 93-100 
    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: In many situations, the most long-ranged parts of the exchange and correlation holes surrounding an electron cancel one another. Apparently for this reason, local spin density and generalized gradient approximations are more accurate for exchange and correlation together than for either alone. A study is made of the ability of these density functionals, and also the unmodified second-order gradient expansion, to describe various short-range effects in atoms: the correlation contribution to the interacting kinetic energy, the antiparallel-spin correlation energy, and the correction to the random phase approximation. Generalized gradient approximations, constructed with no adjustable parameter from the electron gas of slowly varying density, are found to give results of useful accuracy for real atoms. Prospects are discussed for use of the new functionals to improve the accuracy of electronic-structure calculations. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560480813
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    Third-order Møller-Plesset perturbation theory of electron correlation in infinite systems: A comparison of carbon- and silicon-based polymers (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 131-146 
    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: The structural and electronic properties of polysilane, (SiH2)x and polysilene, (SiH)x will be compared with their carbon-based analogues polyethylene, (CH2)x, and polyacetylene, (CH)x, as investigated by the ab initio crystal orbital method using several, partly highly polarized, atomic basis sets of increasing size at the Hartree-Fock (HF) level and by including electron correlation effects up to the third order of Møller-Plesset perturbation theory. The single-particle energy bands have also been corrected for correlation effects applying the electron polaron quasiparticle (QP) method. Electron correlation plays an essential role in stabilizing the gauche conformation of polysilane against the trans form. While the gauche-trans energy difference is about 0.25 mH at the HF level, it will be reduced to about -0.8 mH due to correlation. Also the energy bands and band gaps will be substantially modified in going from the HF to the QP description, resulting in ΔEgap = 9.5 and 11.8 eV for trans and gauche polysilane at HF, and 5.12 and 5.56 eV at the QP level, respectively. Polysilene turns out to be a semiconductor (similar to polyacetylene) for which bond-alternation energetically stabilizes the semiconducting phase (as compared to the equidistant, metallic one) by 1.4 mH at the HF and by 0.6 mH at the MP2 levels, with bond alternations of ΔR = 0.1327 and 0.0865 Å, respectively. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560480816
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    Correlation corrected band structures of quasi 1D and 2D periodic systems and level distributions of disordered chains; new method with correlation for dynamic nonliner optical properties of periodic polymers (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 111-129 
    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: In this paper, methods of correlation corrections for 1D and 2D periodic systems as well as for 1D nonperiodic polymers are reviewed. These procedures include not only the correlation correction of the total energy per unit cell, but also the recalculation (using the generalized electronic polaron model) of the band structures themselves in the periodic case, as well as the density of states (DOS) in nonperiodic chains. In both cases the inverse Dyson equation was used in an iterative way in the MP/2 and MP/3 level. The programming of the same procedure for the coupled cluster method is in progress. In a number of examples (ground state properties of (SN)X, the gap of alternating trans-polyacetylene, the exciton spectrum of diacetylene, polyglycine and polyalanine, of a cytosine stack, the bulk modules of polyethylene, the hopping conductivity of insulin), we have obtained quite good agreement with experiment, if a good basis set ab initio calculation was supplemented of the correlation correction at the bands or DOS curves, respectively. In the second part of the paper a new method is developed to take into account the simulataneous effect of a static and a periodic time-dependent electric field on the one-electron wave functions and on the total electronic energy of a periodic polymer. The method uses a variational technique (coupled Hartree-Fock equations) instead of perturbation theory for the time-dependent one-electron wave functions. The proper treatment of the potential caused by the field, which in this way does not destroy the periodicity of the polymer, as well as the inclusion of correlation at the MP/2 level of the t-and ω-dependent quasienergy per unit cell is part of the method. Finally, it is shown how one obtains in the usual way the different polarizabilities, second- and third-order hyperpolarizability tensor elements with the help of the derivatives of the quasienergies according to the different field (both static and time-dependent) components. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480815
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    Accurate computation of eigenfunctions for Schrödinger operators in one dimension (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 47 (1993), S. 405-423 
    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: A numerical method is developed to obtain sequences of functions converging to the eigenfunctions of a Schrödinger operator in the Hilbert space L2(-∞, ∞), whose norm is used to introduce the criterion of convergence in the norm and we show that it guarantees the accurate computation of expected values of a symmetric operator. The method consists in solving the Dirichlet problem associated to the eigenvalue problem in the interval [-n, n] by the Ritz method, whose convergence to both eigenvalues and eigenfunctions is guaranteed by the compactness criterion. Using the asymptotic perturbation theory in L2(-∞, ∞), we prove the convergence of both eigenvalues and eigenfunctions of the Dirichlet problem to those of the unbounded system when the interval [-n, n] is expanded. The method is applied to the harmonic oscillator, the Mitra potential, as well as to the potential V(r) = r and the Coulomb and Yukawa potentials; in each case, the convergence of eigenvalues and eigenfunctions is shown. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Tab.
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    URL: http://dx.doi.org/10.1002/qua.560470602
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    Relativistic theory for indirect nuclear spin-spin couplings within the polarization propagator approach (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 47 (1993), S. 425-435 
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    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 present a relativistic theory for the nuclear spin-spin coupling tensor within the polarization propagator approach using the particle-hole Dirac-Coulomb-Breit Hamiltonian and the full four-component wave function. We give explicit expressions for the coupling tensor in the random-phase approximation, neglecting the Breit interaction. A purely relativistic perturbative electron-nuclear Hamiltonian is used and it is shown how the single relativistic contribution to the coupling tensor reduces to Ramsey's three second-order terms (Fermi contact, spin-dipole, and paramagnetic spin-orbit) in the nonrelativistic limit. The principal propagator becomes complex and the leading property integrals mix atomic orbitals of different parity. The well-known propagator expressions for the coupling tensor in the nonrelativistic limit is obtained neglecting terms of the order c-n (n ≥ 1). © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560470603
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    Temperature dependence of hydrogen transfer reactions via tunneling at low temperatures (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 47 (1993), S. 437-448 
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    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: In this paper, we present a symmetrical and adiabatic reaction path for hydrogen transfer from methane by methyl by an ab initio method using the 6-31G** basis set with the MP2 corrections for UHF/6-31G** optimized geometries. The theoretical barrier is fitted with the symmetric Eckart function. We, then, take thermal averages of the rate constant (k) considering the discrete nature of the C-H oscillators and the continuous character of the various low-frequency modes of the composite system. Finally, we present a linear relation between log k and temperature. It is shown that this relation gives a good description of the kinetic results of both thermal and photochemical H-transfer reactions in the region of low temperatures. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560470604
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    Eigenvalues of single-cycle class-sums in the symmetric group. II (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 125-134 
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    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: Explicit expressions for the eigenvalues of the single-cycle class-sums [(p)(1)n-p]n of the symmetric group (Sn), with p ≤ 20, are constructed. A new algorithm is used that makes no use of representation-theoretic data. The expressions obtained consist of polynomials in the symmetric power-sums over the “contents” of the Young diagram specifying the irreducible representation, with coefficients that are polynomials in n. On the basis of the results obtained for p ≤ 20, a conjecture is proposed concerning the general form of the four leading terms in these polynomials. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480205
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    Early stages of LiX, BeH2X, and BH3X pyrolysis (X stands for NH3 or OH2): A theoretical study of weak dative complex stability (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 89-108 
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    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: In this work, we study theoretically the thermal decomposition of weak dative complexes (namely, the complexes between BH3, BeH2, or LiH and ammonia or water). The most accurate calculations have been carried out at the MP4sdtq/6-311++G(3df,2p) level on MP2full/6-31G** fully optimized geometries. The transition structures for hydrogen evolution are described. The rate constants were obtained using conventional transition-state theory. Stability conditions for the complexes were considered. Water complexes are less stable than are the corresponding ammonia derivatives. Lithium complexes seem to be very unstable. It seems that beryllium compounds could be synthesized. Borane derivatives are known experimentally. We find, as observed, that the first hydrogen evolution occurs only above room temperature. Iminoborane seems not to be easily accessible under pyrolysis conditions. Other reactions require less activation energy. Finally, the early stages of the ammonia-borane pyrolysis and paths to open-chain polymers as well as to cyclic structures are described. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560480203
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    Computation of auxiliary functions in STO molecular integrals up to arbitrary accuracy. I. evaluation of incomplete gamma function En(x) by forward recursion (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 3-14 
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    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: A new inequality and an approximate relation of incomplete Gamma function En(x) are derived in this paper. Applying both to simplify the error analysis on the recursive algorithm of En(x), we analytically derived a criterion about relative error. The criterion decides whether the forward recursive relation can be used to compute {En(x), n = 0, 1, ⃛, N} with an acceptable loss of significant figures. Further analytical exploration leads to another criterion that decides whether the group of En(x) can be evaluated with an acceptable absolute error by the same methods. Both criteria are not only superior to those given in previous work by other authors, but also strongly supported by our numerical experiments. A strategy is illustrated to explain how to apply both criteria to evaluate molecular integral over Slater-type orbitals. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450103
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    Benchmark values for two-center Coulomb integrals over slater-type orbitals (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 21-30 
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    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: The Löwdin α-function method, in which displaced orbitals are expanded in an infinite series of spherical harmonics, is implemented for Slater-type orbitals using a commercial computer algebra program, Mathematica, The program, which is included, generates a C matrix with integer elements that characterizes our approach to multicenter molecular integrals. The general two-center, two-electron Coulomb repulsion integral is produced analytically with a finite number of terms. Each Coulomb formula may be evaluated to arbitrary precision, since Mathematica works with integer arithmetic. Hence, cancellation errors can be overcome. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450105
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    Variational principle for transition matrix (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 71-85 
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    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: A variational principle for the transition matrix is considered. Conception of the MC SCF (in particular, CASSCF) approach for the transition matrix is proposed as a solution of the variational problem on the optimal evolution of a packet of two stationary states with some additional conditions. An ordinary MC SCF method for a single state is a special case of the proposed approach. Some aspects of the solving of the equations for the optimal transition matrix are treated. The method can be used in atomic and molecular calculations of transition energies, oscillator strengths, and other properties. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450110
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    Closure property for free electrons (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 105-114 
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    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: Some operators considered conventionally as Hermitian are not strictly Hermitian for the freeelectron states known especially in the case of solids. The consequences of this fact on the closure property are examined. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450113
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    Announcement (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 115-117 
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    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450114
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    Masthead (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993) 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450101
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    International journal of quantum chemistry - a journal devoted to quantum theory and computations in chemistry, condensed matter physics, and biology. Editorial - program and policies (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 1-2 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450102
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    A first-principles approach to high-Tc superconductivity. II. The superconducting ground state (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 201-209 
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    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 show that a consistent N-electron theory of a solid can within the Born-Oppenheimer (BO) approximation lead only to normal conductivity or to an insulating state. If one leaves the BO approximation by turning on electron-phonon interaction, one can establish a lower-lying new ground state that has the characteristic properties of the Bardeen-Cooper-Schrieffer (BSC) ground state. We demonstrate that an (N + Nn)-particle Schrödinger equation that describes the motion of N electrons and Nn nuclei of a solid can lead only to phonon-induced superconductivity. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480305
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    Masthead (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993) 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480401
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    Ground and first excited states of fractionally charged sodium atoms (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 219-224 
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    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: The energy levels in sodium atoms with quarks attached to the nucleus are obtained using the configuration interaction method. It is found that the calculated 3p (2P) → 3s (2S) electronic transition in the Na-1/3 quark-atom system is in agreement with that predicted by extrapolation of experimental data. Also, ionization potentials of fractionally charged sodium atoms are discussed. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480402
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    To(Γ) phonons in GaAs under uniaxial strain (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 43-49 
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    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: Using the density-functional theory in the local-density approximation, norm-conserving pseudopotentials, and plane-wave expansions, we have developed a simple way to calculate ab initio the uniaxial strain dependence of the TO(Γ) phonon mode in GaAs, including the envolved relaxations effects. The relaxation response of the system was evaluated from the use of the elasticity theory. Our results confirm the experimental evidence and show a reasonable agreement with the observed data for the frequency splitting of this phonon mode. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450107
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  • 92
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    Electric-field mapping of some anions and cations of adenine and guanine (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 233-238 
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    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: Electric-field maps of certain anions and cations of adenine and guanine have been studied. The results are compared with those of neutral adenine and guanine. In all cases, the geometries were fully optimized using the MNDO molecular orbital method and the fields were computed using Mulliken charges. Reactivities and hydrogen-bonding pattern predicted by electric fields, including those of cations, are in satisfactory agreement with experiment. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480404
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    Multiplication theorems for orthogonal polynomials (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 239-247 
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    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: In this paper, a general method is presented that allows the derivation of the expansion coefficients of the product of two orthogonal functions provided the generating function is known. For the three classical orthogonal polynomials, the Laguerre, the Hermite, and the Legendre polynomials, the coefficients blmn with φmφn = ∑lblmnφl are derived. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480405
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    Finding transition states when second-order Jahn-Teller instability occurs (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 211-218 
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    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: When second-order Jahn-Teller couplings become strong along “streambeds” on potential energy surfaces, instability reflected in negative curvature along a symmetry-lowering distortion coordinate can take place. The point where such negative curvature sets in is usually not a transition state because the gradient of the potential is usually large there. In this paper, it is demonstrated how to use the local energy, local gradient, local Hessian, and knowledge of how quickly the curvature for the symmetry-breaking mode evolves along the streambed (i.e., the derivative of this curvature) to predict how far to move in the symmetry-breaking mode in search of the desired transition state. It is shown that the Hessian matrix evaluated at the symmetry-broken geometry suggested by this analysis has only one negative eigenvalue. Because this analysis is based on a local approximation to the potential, its predictions are, of course, approximate. As such, they only “suggest” the proper direction and magnitude that one should “step” to move toward a transition state. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480306
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  • 95
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    Perturbation theory to determine the stable isomer of triatomic linear molecules (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 249-256 
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    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: The electronegativity perturbation theory up to the fourth order has been used to study the preferred isomer of linear triatomic molecules. Systems with 10-16 valence-electron systems are discussed and our results are in good agreement with the experiment. The only exception is the isomers of PNO. The usefulness of the perturbation theory is briefly discussed. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480406
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  • 96
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    Electronic Resource
    Masthead (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993) 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450201
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  • 97
    Electronic Resource
    Electronic Resource
    Half-projected Hartree-Fock natural orbitals for defining CAS-SCF active spaces (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 133-166 
    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 have extended the range of systems to which the half-projected Hartree-Fock (HPHF) method has been applied, including the triplet state of the wave function. In our implementation, DIIS overcomes the convergence difficulties reported in earlier studies. HPHF allows generation of a symmetry-broken wave function in regions of the potential energy surface where the RHF wave function is triplet-stable. The fractionally occupied natural orbitals (FONOS) of the HPHF wave function are good starting vectors for CAS-SCF calculations. A CAS-SCF in the space defined by the HPHF FONOS should be used instead of the unrestricted natural orbital CAS-SCF method in regions of triplet stability and for small active space problems. We draw extensive comparisons between the results of both the UNO-CAS and HPNO-CAS methods and those of full CAS-SCF calculations. © 1993 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450203
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  • 98
    Electronic Resource
    Electronic Resource
    Icons and symmetries. By Simon Altmann, Oxford University Press, Oxford, 1992 (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 225-225 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450208
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  • 99
    Electronic Resource
    Electronic Resource
    Multipole moment analysis for hydrides, fluorides, and lithium compounds of first- and second-row elements (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 295-308 
    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: A method is presented that conserves all local dipole moments in a partitioning of overlap charge between pairs of atoms. The approximate conservation of quadrupole and higher-moment components can be used as a criterion for the suitability of atomic basis sets. Ab initio calculations are presented for hydrides, fluorides, and lithium compounds of first- and second-row elements in a systematic study of compounds and basis sets. The best suitable basis set for each series is determined by the criterion of best approximate conservation of quadrupole moment components. A linear relation between charge shifts and Mulliken electronegativity differences is established for diatomic molecules. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480504
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  • 100
    Electronic Resource
    Electronic Resource
    Masthead (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993) 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480601
    Library Location Call Number Volume/Issue/Year Availability
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