Journal
MOLECULAR PHYSICS
Volume 104, Issue 8, Pages 1191-1206Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1080/00268970600571377
Keywords
local correlation; static correlation; coupled cluster theory
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Inspired by the success of very restrictive local active space approaches like Generalized Valence Bond Perfect Pairing (GVB-PP) and Imperfect Pairing (IP), we investigate the localizability of valence correlation in the context of electron pair models. In particular, the role of two-center local excitations in local active space coupled cluster doubles models is examined in the context of a variety of chemical applications. The full two spatial center pairing model is found to recover the majority of the correlation effects missed by GVB-PP and IP, recovering up to 95% of the untruncated valence correlation energy, and could provide an inexpensive reference wave function for the treatment of additional electron-electron correlations. All of these models improve noticeably upon the Hartree-Fock wave function and can be computed for very large systems due to their only cubic computational cost. Their main weakness is a tendency to exhibit symmetry breaking in systems with multiple resonance structures.
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