Degeneracy breaking in the Hilbert-space coupled cluster method

Sigalit Berkovic*, Uzi Kaldor

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The Hilbert space multireference coupled cluster method with single and double excitations (HS-MRCCSD) is applied to excited states of the N2 molecule. Particular attention is given to the breaking of degeneracy, where sublevels which should be degenerate by symmetry come out separated by as much as 0.3 eV. This feature is explained by the fact that a truncated coupled cluster expansion starting from an open-shell determinant does not preserve spin or spatial symmetry.

Original languageEnglish
Pages (from-to)3090-3094
Number of pages5
JournalJournal of Chemical Physics
Issue number4
StatePublished - 1993


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