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  • 1
    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
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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)
    Fulltext
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