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  • 1
    Electronic Resource
    Electronic Resource
    Direct calculation of the energy gradient with cartesian Gaussian basis sets (1976)
    Springer
    Theoretical chemistry accounts 41 (1976), S. 217-221 
    Details
    ISSN: 1432-2234
    Keywords: Energy gradient ; Differentiation of electronic integrals, analytical ∼
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A computer program POLYGRAD based on the POLYATOM/1 system is presented which evaluates analytically the energy gradient using thes-type and Cartesianp-type Gaussian basis functions. Model calculations on hydrogen peroxide were made to compare the accuracy and the computer time involved in the analytical and numerical determinations of the energy gradient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01151956
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Restricted Hartree-Fock and unrestricted Hartree-Fock as reference states in many-body perturbation theory: a critical comparison of the two approaches (1991)
    Springer
    Theoretical chemistry accounts 80 (1991), S. 407-425 
    Details
    ISSN: 1432-2234
    Keywords: Many-body perturbation theory ; Hartree-Fock ; Potential surfaces ; Open-shell systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The paper deals with two topics related to the problem which reference state is better for many-body perturbation theory: restricted Hartree-Fock (RHF) or unrestricted Hartree-Fock (UHF)? The first topic concerns the potential surfaces. Several examples are presented to show shortcomings of the two approaches and a simple way is presented which seems to give a useful potential curve in the whole range of interatomic distances by a composition of RHF and UHF potential curves. The second topic concerns the many-body perturbation theory for open-shell systems in the RHF formalism. The method is critically examined and compared with the ordinary many-body perturbation theory using UHF as the reference. This examination of many-body techniques provides also some insight into the problems inherent of the SCF theory: spin contamination from higher multiplets, localization of orbitals, and self-consistency effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01117420
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Correlation energies in open shell systems. Comparison of CEPA, PNO-CI and perturbation treatments based on the restricted Roothaan-Hartree-Fock formalism (1982)
    Springer
    Theoretical chemistry accounts 60 (1982), S. 445-450 
    Details
    ISSN: 1432-2234
    Keywords: Correlation energy of radicals ; Many-body perturbation theory ; CEPA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A set of simple molecules in closed and open-shell ground states is treated by the three techniques mentioned in the title, using the same geometries and basis sets (DZ + P). It is found that for nearly all molecules treated in this study (exceptions are H2 and CH3) consistently about 98% of the CEPA valence shell correlation energy is obtained by third-order many-body Ray-leigh-Schrödinger perturbation theory (MB-RSPT). The CEPA and MB-RSPT results for reaction energies and barrier heights for some simple reactions differ by 0 to 30 kJ/mol, the CEPA results being in most cases closer to experiment than MB-RSPT, while CI results are much less reliable as long as CI is limited to singly and doubly substituted configurations only.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00548697
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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