Theoretica chimica acta

, Volume 60, Issue 5, pp 445–450 | Cite as

Correlation energies in open shell systems. Comparison of CEPA, PNO-CI and perturbation treatments based on the restricted Roothaan-Hartree-Fock formalism

  • Petr Čársky
  • Ivan Hubač
  • Volker Staemmler
Original Investigations


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.

Key words

Correlation energy of radicals Many-body perturbation theory CEPA 


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Copyright information

© Springer-Verlag 1982

Authors and Affiliations

  • Petr Čársky
    • 1
  • Ivan Hubač
    • 2
  • Volker Staemmler
    • 3
  1. 1.J. HeyrovskΫy Institute of Physical Chemistry and ElectrochemistryCzechoslovak Academy of SciencesPrague 2Czechoslovakia
  2. 2.Department of Biophysics, Faculty of Mathematics and PhysicsComenius UniversityBratislavaCzechoslovakia
  3. 3.Lehrstuhl für Theoretische Chemie der Ruhr-Universität BochumBochumFederal Republic of Germany

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