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  • 1
    Electronic Resource
    Electronic Resource
    Steric Overcrowding in Perhalogenated Cyclohexanes, Dodecahedranes, and [60]Fulleranes (1995)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 10381-10384 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00146a024
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  • 2
    Electronic Resource
    Electronic Resource
    Electron intracule densities with correct electron coalescence cusps from Hiller–Sucher–Feinberg-type identities (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 6093-6103 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Identities for the electron intracule density I(R) in atoms and molecules are derived within the Hiller–Sucher–Feinberg (HSF) formalism. It is proven that, when applied to arbitrary (exact or approximate) electronic wave functions, these identities produce intracule densities that satisfy a modified condition for the electron coalescence cusp. A corollary of this proof provides a new, simplified derivation of the cusp condition for the exact I(R). An expression for the Hartree–Fock approximation to the HSF electron intracule density that contains only two- and three-electron terms is obtained and its properties are analyzed. A simple scaling of the three-electron contributions in this expression assures integrability of the approximate I(R) and improves its overall accuracy. Numerical tests carried out for the H−, He, Li+, Be2+, Li, and Be systems demonstrate that the application of the scaled HSF-type identity to Hartree–Fock wave functions affords dramatic improvements in the short-range behavior of the electron intracule density. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470437
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  • 3
    Electronic Resource
    Electronic Resource
    Photoabsorption of the peroxide linkage defect in silicate glasses (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 8039-8042 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: First-principles quantum chemical techniques on cluster models have been used to investigate the photoabsorption of the peroxide linkage defect in silicate glasses. The effects of geometry, basis sets, and cluster size have been considered carefully to derive converged values for the low-lying excitation energies. The lowest singlet-to-singlet transition is a weak absorption at 5.5 eV. A stronger valence absorption occurs at 6.8 eV. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480137
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  • 4
    Electronic Resource
    Electronic Resource
    Analytical derivatives of atomic zero-flux surfaces and properties of atoms in molecules with respect to external perturbations (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 8741-8747 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A complete theory of the response of the atomic zero-flux surfaces to external perturbations is presented. The resulting expressions for the analytical derivatives of the properties of atoms in molecules (AIMs) are implemented in an efficient computer code. Several test calculations demonstrate the clear advantages of the new approach over methods based upon numerical differentiation. The present development opens an avenue to routine calculations of the second-order response properties of AIMs. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472653
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  • 5
    Electronic Resource
    Electronic Resource
    Accurate thermochemistry for larger molecules: Gaussian-2 theory with bond separation energies (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 6764-6767 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Gaussian-2 (G2) theory is combined with isodesmic bond separation reaction energies to yield accurate thermochemistry for larger molecules. For a test set of 40 molecules composed of H, C, O, and N, our method yields enthalpies of formation, ΔHf0(298 K), with a mean absolute deviation from experiment of only 0.5 kcal/mol. This is an improvement of a factor of three over the deviation of 1.5 kcal/mol seen in standard G2 theory.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473659
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  • 6
    Electronic Resource
    Electronic Resource
    Pathways for initial water-induced oxidation of Si(100) (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 824-826 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: First-principles molecular orbital methods and gradient-corrected density functional calculations on silicon clusters are used to study possible pathways for the initial oxidation of Si (100)-2×1. In these reactions, the adsorbed hydroxyl oxygen inserts into the dimer Si–Si bond to form a suboxide ((Triple Bond)Si–O–Si(Triple Bond)) surface structure. The reaction typically follows a two-step pathway involving an intermediate energy minimum. In the case of an ideal surface with full water coverage, the reaction is exothermic by 1.3 eV and the overall reaction barrier is estimated at 2.4 eV. However, an alternative pathway involving a dangling bond site lowers the activation barrier to 2.1 eV. The implications for the oxidation reaction rates are discussed as well as possible alternative pathways. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122013
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  • 7
    Electronic Resource
    Electronic Resource
    Electron flow and electronegativity equalization in the process of bond formation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 5151-5162 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Charge-constrained calculations make it possible to rigorously analyze electron flow and electronegativity equalization in the process of bond formation. Such an analysis is performed for the prototypical H2, HF, and LiH molecules. As the bonds are stretched, the dependence of the electronegativity difference on the extent of charge transfer undergoes a transition from approximate linearity to a steplike discontinuous character. With the help of the second-order perturbation theory, the bond hardness is related to the matrix elements of the fragment-electron-count operator and is shown to increase exponentially with the bond length R at the dissociation limit. For polar bonds, the magnitude of the in situ electronegativity difference ΔχAB decreases quickly with R due to the decreasing polarization of the fragments. However, ΔχAB levels off for large distances, and most of the reduction in charge transfer that accompanies bond dissociation can be attributed to the dramatic increase in the bond hardness. The charge-constrained calculations provide both the evidence and explanation for the energy derivative discontinuities that are observed in isolated atoms and molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466016
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  • 8
    Electronic Resource
    Electronic Resource
    Cluster models for the photoabsorption of divalent defects in silicate glasses: Basis set and cluster size dependence (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 770-772 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The two lowest singlet excited states of divalent Si defects in silicate glasses are studied by ab initio methods. Excitation energies of 5.2 and 6.8 eV are obtained. Steady convergence to these values is shown with the increase in size both of the model cluster and of the basis set employed in the calculations. The results clearly demonstrate the viability of the quantum-chemical cluster approach for the study of local excitations in glass defects. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120422
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  • 9
    Electronic Resource
    Electronic Resource
    An efficient approach to calculation of zero-flux atomic surfaces and generation of atomic integration data (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 16 (1995), S. 1394-1404 
    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: A new robust method for variational determination of atomic zero-flux surfaces is presented. The zero-flux surface sheets are expressed in terms of variational trial functions in prolate spheroidal coordinates. The trial functions are optimized with a Newton procedure to satisfy the zero-flux condition on a grid. The data required for radial integrations are generated by an adaptive quadrature procedure that employs model electron densities and utilizes an original third-order algorithm for linear search. Results of test calculations involving variational determination of atomic surfaces are presented for a representative set of 20 molecules. The new approach is both less time consuming and substantially more accurate than the previously published algorithms. © 1995 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540161108
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  • 10
    Electronic Resource
    Electronic Resource
    Efficient algorithm for quantitative assessment of similarities among atoms in molecules (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 1352-1358 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A new algorithm for quantitative assessment of similarity between two atoms in molecules is presented. Both the atomic similarity index and its derivatives with respect to the three Euler angles that describe the mutual orientation of the atoms under comparison are computed efficiently by taking advantage of the recently developed analytical representations for atomic zero-flux surfaces. The use of such representations makes it possible to substantially enhance the accuracy of the computed similarity indices without increasing the cost of their evaluation. Numerical tests involving oxygen atoms in several carbonyl compounds demonstrate the ability of the new algorithm to discern small changes in atomic similarity that are brought about by second-neighbor effects. Comparisons among hydrogen atoms in the acrolein molecule reveal the usefulness of the similarity index in detection and quantification of the effects of steric interactions on atomic shapes. © 1996 by John Wiley & Sons, Inc.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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