title: Coupled-Cluster Valence-Bond Singles and Doubles for Strongly Correlated Systems: Block-Tensor Based Implementation and Application to Oligoacenes.
abstract: We demonstrate a block-tensor based implementation of coupled-cluster valence-bond singles and doubles (CCVB-SD) [Small, D. W.; Head-Gordon M. J. Chem. Phys. 2012, 137, 114103] which is a simple modification to restricted CCSD (RCCSD) that provides a qualitatively correct description of valence correlations even in strongly correlated systems. We derive the Λ-equation of CCVB-SD and the corresponding unrelaxed density matrices. The resulting production-level implementation is applied to oligoacenes, correlating up to 318 electrons in 318 orbitals. CCVB-SD shows a qualitative agreement with exact methods for short acenes and reaches the bulk limit of oligoacenes in terms of natural orbital occupation numbers, whereas RCCSD shows nonvariational behavior even for relatively short acenes. A significant reduction in polyradicaloid character is found when correlating all valence electrons instead of only the π-electrons.
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Joonho
authors.identifier: http://orcid.org/0000-0002-9667-1081
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: David W
authors.initials: DW
authors.lastname: Small
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Evgeny
authors.initials: E
authors.lastname: Epifanovsky
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Martin
authors.identifier: http://orcid.org/0000-0002-4309-6669
authors.initials: M
authors.lastname: Head-Gordon