Improving CISD calculations by geminal-type reference states

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

The possibility of using geminal-type wavefunctions as multi-configurational reference states for configuration interaction (CI) calculations is investigated. The reference function class considered here includes 2-electron CAS, certain types of MC-SCF and APSG (antisymmetrized product of strongly orthogonal geminals) as special cases. The method is not variational but exact for two electrons. The relation between the developed formalism and GVB-CI, internally contracted multi-reference CI (IC-MRCI) and EOM-CC techniques is discussed. We present applications at the CISD level. The results show that total energies generally fall between standard CISD and CCSD values. The proposed modification of CISD decreases the size-consistency error and eliminates it if the molecule is fragmented into two-electron pieces. Preliminary calculations show an appreciable improvement of CISD dissociation energies.

Original languageEnglish
Pages (from-to)221-228
Number of pages8
JournalChemical Physics Letters
Volume312
Issue number2-4
Publication statusPublished - Oct 22 1999

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configuration interaction
Electrons
Wave functions
electrons
self consistent fields
Molecules
dissociation
formalism
energy
products
molecules

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Spectroscopy
  • Atomic and Molecular Physics, and Optics

Cite this

Improving CISD calculations by geminal-type reference states. / Kállay, M.; Surján, P.

In: Chemical Physics Letters, Vol. 312, No. 2-4, 22.10.1999, p. 221-228.

Research output: Contribution to journalArticle

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