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  • Computational Chemistry and Molecular Modeling  (8)
  • Additivity model  (1)
  • Helium isoelectronic sequence, screening in the ∼  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Scaling in the S and P states of the helium isoelectronic sequence (1974)
    Springer
    Theoretical chemistry accounts 33 (1974), S. 79-86 
    Details
    ISSN: 1432-2234
    Keywords: Atomic screening constants ; Mean values of r 1 r and r 12 r in two-electron atoms ; Scaling ; Helium isoelectronic sequence, screening in the ∼
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Mean values of r 1 r and r r 12 for the ground and several excited states of the helium isoelectronic sequence are used to demonstrate that a simple scaling which superimposes the distribution function f(r 12) as a function of the atomic number leads to a similar result for the electron density distribution D(r1). On the basis of a screening interpretation of the scaling parameter δ, it is concluded that screening is greater in the singlet than the triplet state of a particular configuration, that screening is greater in the P states than the corresponding S states, and that the screening approaches the limiting value of 1 for the highly excited states. The perturbation expansions of Scherr and Knight are used to determine the limiting value of δ when Z→∞ and the relationship between the scaling parameter and the scale factor, chosen so that a trial wave function satisfies the virial theorem, is discussed. A brief discussion of the scaling of the Coulomb hole is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00527627
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  • 2
    Electronic Resource
    Electronic Resource
    Additivity model calculations of UHF spin densities and charge densities in methyl-substituted radical cations (1979)
    Springer
    Theoretical chemistry accounts 53 (1979), S. 309-317 
    Details
    ISSN: 1432-2234
    Keywords: Additivity model ; UHF spin densities and charge densities ; Heteroatom model ; Radical cations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract By use of a heteroatom model for the methyl group and an additivity model for spin densities, the unrestricted Hartree-Fock after annihilation (UHFAA) results for the radical cations of naphthalene, 1-methylnaphthalene and 2-methylnaphthalene are used to predict the spin densities in the π-electron approximation in the corresponding cations of di-, tri- and tetramethylnaphthalenes. The additivity model approach is shown to be equally successful for charge densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00555690
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Ab-initio molecular orbital study of the cis/trans conformations of the peptide bond (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 20 (1981), S. 117-127 
    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: Ab-initio molecular orbital (MO) calculations on the model peptide, N-methylacetamide (NMA), protonated N-methylacetamide (p-NMA), and two natural dipeptides, glyclyglycine (Gly-Gly) and alanylalanine (Ala-Ala), are reported. Calculations at the STO-3G. 3-21G. and 4-31 G levels account for the predominance of the trans conformation in globular proteins. By use of p-NMA as a model precursor, the formation of the peptide bond is studied by the methods of molecular quantum mechanics. These calculations lead to the conclusion that the trans conformation should predominate, in agreement with the crystal structural data on globular proteins. In order to reduce the amount of computer time required for what are evidently the first ab-initio MO calculations on natural dipeptides, force-field calculations have been employed to obtain the conformational potential energy maps.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560200710
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  • 4
    Electronic Resource
    Electronic Resource
    Angular aspects of exchange correlation and the fermi hole (1985)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 27 (1985), S. 439-449 
    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 complete (nonreduced) αα probability density functions evaluated from the Hartree-Fock and simple Hartree product wavefunctions have been used to elucidate the angular features of spin correlation and the Fermi hole in the 23S state of helium and the ground state of beryllium. This approach shows that the local Fermi holes in these two cases are very similar and that the Fermi hole is essentially spherically symmetric when the reference electron is close to the nucleus. As the reference electron is removed to larger radial distances, appreciable polarization of the Fermi hole is observed. The polarization is greater in the direction of the nucleus than away from the nucleus, contrary to the situation in the Coulomb hole of the helium ground state where the polarization is greater away from the nucleus than toward the nucleus. Several other differences between the He 23S Fermi hole and the He 11S Coulomb hole are noted.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560270408
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  • 5
    Electronic Resource
    Electronic Resource
    On the relationship between the electron-pair distribution function and the correlation energy of an atom (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1-9 
    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 pair distribution function h(r12;r1, γ) and the virial theorem are used to derive a general expression for the local contributions to the total correlation energy of an atom. A direct link between correlation effects and the correlation energy is obtained by use of G(r1, γ) and Γ(r1, y). The former is the probability associated with a given choice of r1 and γ, while the latter describes the local contribution to the correlation energy. Explicit calculations for the ground state of helium indicate that the angular dependence of the local contribution to the correlation energy is essentially independent of r1, whereas the local correlation energy shows a strong r1 dependence. The maximum contribution to the correlation energy occurs at intermediate values of γ where there is close agreement between the Hartree-Fock and exact densities.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290102
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  • 6
    Electronic Resource
    Electronic Resource
    Statistical electron correlation coefficients for 29 states of the heliumlike ions (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 33-42 
    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: Statistical electron correlation coefficients provide overall measures of the difference between the electron pair density and the product of one-electron densities. Explicitly correlated wave functions are used to compute radial and angular correlation coefficients for 29 low-lying states (n1S, n3S, n1P, n3P, n1D, and n3D with n 〈 7) of the two-electron ions from helium through Ne8+. This data base of 1566 correlation coefficients permits a systematic study of trends with respect to variation of nuclear charge, degree of excitation, angular momentum, and spin multiplicity. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480807
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Ab initio and molecular dynamics study of dibenzotricyclic calcium antagonists: A rigid model approach (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 17-31 
    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 class of calcium antagonists (dibenzotricyclic compounds) is studied by means of reaction field ab initio calculations and molecular dynamics simulations. The central ring of these tricyclic molecules is found to be more important to the calcium antagonistic potency than the two phenyl rings. The central ring with antagonistic potency shows hydrophobic character, thus the interaction between the drug and the binding sites is assumed to be dominated by hydrophobic interactions. Variation of the flexure angle, the angle between the two phenyl rings, does not change the hydrophobic property of the central ring significantly, therefore it is not expected to affect the interaction between the drug and binding site directly. The effect of the flexure angle on calcium antagonistic potency, the relation between drug affinity of these tricyclic molecules and their ionization energies, and the interaction of calcium ions with the central ring are discussed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520704
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  • 9
    Electronic Resource
    Electronic Resource
    The effect of electron correlation on the topological and atomic properties of the electron density distributions of molecules (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 10 (1989), S. 367-375 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The topological properties of the electron density and the properties of an atom in a molecule are calculated by means of second-order Møller-Plesset perturbation theory (MP2) and compared with the results of configuration interaction calculations (C12) which include all single and double substitutions from the Hartree-Fock reference configuration. A software package for analyzing the effects of electron correlation on the topological properties of the electron density of molecules is described. H2CO is used to provide a numerical example and to indicate that the number of bond critical points is unaffected by the inclusion of electron correlation. Correlation leads to only a small shift in the positions of bond critical points and a small change in the electron density at bond critical points. It is further shown that the energy of an atom in a molecule can be calculated to an accuracy of 1 kcal/mol and the electron population of an atom to about 0.001e. A statistical method is used to show that the deviation of the MP2 correlation correction relative to the CI2 correlation correction for a variety of atomic properties is about 25%.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540100310
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  • 10
    Electronic Resource
    Electronic Resource
    Bond critical points in the electronic structures of the main group diatomic hydrides of lithium through bromine (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 8 (1987), S. 489-498 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The bond critical points and associated electronic properties of the diatomic hydrides of the twenty-one main group elements from lithium to bromine have been calculated with large basis sets. As part of a systematic study of the polarity of chemical bonds, the position of the bond critical point, the charge density at the bond critical point, the Laplacian of the charge density at the bond critical point, and the molecular dipole moment of each molecule have been calculated. Particular attention has been paid to the effect of bond length elongation and contraction on the electronic properties. Variation of the bond length reveals that with atoms of low electronegativity, the bond critical point of AH tends to follow atom A, whereas with atoms of high electronegativity, the bond critical point tends to follow the hydrogen atom as the bond lengthens. Furthermore, it is shown that some properties of the diatomic hydrides vary monotonically within each row of the periodic table, while others effect a classification according to the character of the bond.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540080429
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