Hilbert space coupled-cluster method in an incomplete model space

Sigalit Berkovic, Uzi Kaldor

Research output: Contribution to journalArticlepeer-review


The Hilbert space multireference coupled-cluster method with single and double excitations (HS-MRCCSD) is implemented in complete and special classes of incomplete model spaces. Vertical excitation energies of the water molecule are calculated. Good agreement (within 0.1 eV) is obtained with experimental values, and also with results of Fock space calculations which include effects of triple excitations in lowest order (FS-MRCCSD+T). The HS-MRCCSD functions are not pure spin states, and small energy differences occur between sublevels which should be degenerate.

Original languageEnglish
Pages (from-to)42-46
Number of pages5
JournalChemical Physics Letters
Issue number1-2
StatePublished - 30 Oct 1992


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