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  • 1
    Electronic Resource
    Electronic Resource
    Reduction of the computational effort in quantum Monte Carlo calculations with pseudopotentials through a change of the projection operators (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 459-463 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The usual form of nonlocal pseudopotentials which project the wave function on real spherical harmonics is inconvenient in quantum Monte Carlo calculations because the projection integrals are still functions of r. It is thus necessary to calculate the integral in every point of the simulation. We circumvent this problem by transforming the pseudopotential to a form where the projection occurs on Cartesian Gaussian-type functions which makes the projection integrals independent of the electron coordinates. We applied our method to two-valence electron systems using the pure diffusion method, where the approximation in the pseudopotential is the only one present.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463591
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  • 2
    Electronic Resource
    Electronic Resource
    Contribution to the electron distribution analysis. I. Shell structure of atoms (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1928-1942 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Relativistic spherically averaged numerical all-electron densities ρ were computed for the atoms Be–Ba, B–Tl, C–Pb, Cu–Au, and Zn–Hg. The Laplacian of these densities is not able to resolve the valence shell from the inner shells in case of heavy atoms, starting with the fourth row. The distribution of the local kinetic energy Ekin shows a valence maximum even for these heavy atoms, unfortunately, in a region of negative kinetic energy; i.e., nonclassically allowed. The quantity −||∇ρ||/ρ was also investigated. For all computed atoms, the −||∇ρ||/ρ diagrams are capable of describing the complete shell structure. −||∇ρ||/ρ is sensitive to basis set quality: poor Gaussian basis sets exhibit spurious oscillations and a premature onset of the linear decay. For the atoms B–Tl, Ba, Au, Hg, and Pb, nonrelativistic numerical calculations were performed to examine the effect of the relativity on the aforementioned quantities. Tests with pseudopotential densities reveal that for pseudopotential calculations, it is advisable to use at least two outermost shells in order to reproduce the all-electron values of ∇ 2ρ, Ekin, and −||∇ρ||/ρ in the valence region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460989
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  • 3
    Electronic Resource
    Electronic Resource
    A new Jastrow factor for atoms and molecules, using two-electron systems as a guiding principle (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 691-697 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: To get an idea of the qualitative behavior of an optimal Jastrow factor we have considered a Hylleraas-type wave function of very high accuracy for the helium atom. Owing to the lack of nodes this wave function can be easily interpreted as a general type of Jastrow factor. As a result we obtained a simple parameter dependent ansatz for a Jastrow factor, which incorporates the essential features of the observed behavior. We have optimized the parameters with respect to the variance of the local energy, using variational Monte Carlo techniques, for the atoms He through Ne and for the simple molecules H2, LiH, and Li2. Finally, we compare our approach with other types of Jastrow factors discussed in the literature. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470103
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  • 4
    Electronic Resource
    Electronic Resource
    Correlation energies for some two- and four-electron systems along the adiabatic connection in density functional theory (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 2828-2835 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Switching on the electron–electron interaction connects the Kohn–Sham to the physical system. The correlation energy, the only unknown energy component in this process, is determined at fixed density, using a technique based on the Lieb Legendre transform definition of the universal density functional. Results are shown for this adiabatic coupling process for He,Ne8+,Be,Ne6+ as well as for the exponential densities nN,ζ(r)=N(ζ3/π)e−2ζr (N=2 or 4; ζ≥1; for N=4 degeneracy is present and 1D and 3P are analyzed). The data are fitted to a rational approximant and appear to be in good agreement with those given by the less computationally demanding Harris–Jones adiabatic connection. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478234
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  • 5
    Electronic Resource
    Electronic Resource
    Analysis of the linear response function along the adiabatic connection from the Kohn–Sham to the correlated system (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 6827-6833 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Careful calculations are performed to obtain the radial density–density response function for the He and the Be series. This is also done along the adiabatic connection of the density functional theory (as the system evolves from the real, physical system to the Kohn–Sham one). In this process the electron density is kept constant, while the strength of the interaction between electrons changes. The response functions are analyzed in terms of their eigenvalues and eigenfunctions. The latter change only little along this process. The absolute value of the eigenvalues is in general reduced by the interaction: A screening effect is present. For the near-degenerate systems, we notice that the opposite effect can appear (antiscreening). © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1405011
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  • 6
    Electronic Resource
    Electronic Resource
    Für Ihre Dokumentation von Nr. 3/97 Chemie in unserer Zeit (1997)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 31 (1997), S. 154-154 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19970310312
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  • 7
    Electronic Resource
    Electronic Resource
    Chemische Bindung anschaulich: die Elektronen-Lokalisierungs-Funktion (1997)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 31 (1997), S. 110-120 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The Electron Localization Function (ELF) describes chemical bonding through localized pairs of electrons and gives a quantum mechanical basis to the representation of the chemical bond as a line. Computer graphics produce illustrative and intuitive pictures of the shell structure of atoms, ionic, covalent, and coordinative bonds, or multiple bonds and lone pairs of electrons. Resonance formulas, delocalized bonds, and the space occupied by electron pairs can be visualized in the same manner.
    Notes: Die ELF ist ein Maß für die Abstoßung der Elektronepaare (Pauli-Abstoßung) und kann aus quantenmechen Rechnungen erhalten werden. Mit Hilf dieser Funktion kann man den Raum in Bereiche unterteilen, die man den Elektronenpaaren zuordnet (Elektronenpaarbereiche).
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19970310303
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  • 8
    Electronic Resource
    Electronic Resource
    Virtual space level shifting and correlation energies (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 69 (1998), S. 581-590 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Adding a nonlocal operator to the true Hamiltonian is used to define an adiabatic coupling between a noninteracting (e.g., Kohn-Sham) reference system and the real one. By using the Hellmann-Feynman theorem, it is shown that when the operator added is shifting upward the virtual (noninteracting) levels the correlation energy is related to the number of electrons displaced into the virtual levels. To construct approximations, calculations were performed for the uniform electron gas. The expectation that atomic systems would behave locally like a uniform electron gas with the unoccupied levels shifted up by a constant close to the atomic excitation energies is not confirmed by exploratory calculations on atoms. Some perturbation theory expressions are also given and suggest an approach to self-interaction free-correlation energy functionals.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 581-590, 1998
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Topologische Bifurkationsanalyse: Elektronenstruktur von CH5Wir danken Bernard Silvi und Jürg Hutter für hilfreiche Diskussionen. (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 109 (1997), S. 2168-2170 
    Details
    ISSN: 0044-8249
    Keywords: Ab-initio-Rechnungen ; Elektronenlokalisierung ; Elektronenstruktur ; Hypervalente Verbindungen ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19971091912
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  • 10
    Electronic Resource
    Electronic Resource
    Die Elektronenlokalisierungsfunktion ELFProfessor Hans Georg von Schnering gewidmetDiese Arbeit wurde gefördert vom Schweizerischen Nationalfonds, durch die Projekte Nr. 0-20-851-94, Nr. 0-20-288-96, und das C4-Projekt der ETH Zürich. (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 109 (1997), S. 1892-1918 
    Details
    ISSN: 0044-8249
    Keywords: Bindungstheorien ; Elektronenlokalisierungsfunktion ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die Gesichtspunkte, unter denen die Frage nach der chemischen Bindung gestellt wird, hängen davon ab, welche Verbindungsklassen oder welche chemisch-physikalischen Aspekte behandelt werden sollen, d.h. man wählt jeweils die zum Forschungs- und Anwendungshintergrund passenden Beschreibungsschemata für die chemische Bindung aus. So existieren bedeutende Unterschiede im Verständnis dessen, was chemische Bindung ist. Dieser Umstand führt zu Trennungen, die vielleicht aus praktischen Gründen verständlich, aber im Sinne einer echten Interdisziplinarität sehr hinderlich sind. Dabei bieten gerade die Konzepte der chemischen Bindung eine ungeheuer tragfähige Basis, um nicht nur innerhalb der Chemie, sondern auch zu allen benachbarten Wissenschaften Brücken zu schlagen. Der allgemeine Wunsch nach interdisziplinärer Zusammenarbeit und die zweifellos gewachsene Notwendigkeit hierfür erfordern eine pflegliche Behandlung dieser Konzepte und, wenn möglich, eine Straffung und Vereinheitlichung, die möglichst vielen akzeptabel erscheint und hilfreich wird. Wir glauben, daß die Elektronenlokalisierungsfunktion (ELF) in der Ära einer lawinenartigen Computer- und Informatikentwicklung eine neue Beschreibung der chemischen Bindung für nahezu alle Stoffklassen ermöglicht und durch ihre Bildsprache entscheidend zu einer erweiterten Interdisziplinarität beitragen sollte.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19971091706
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