Journal
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
Volume 13, Issue 2, Pages 602-615Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jctc.6b01092
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Funding
- ARO MURI Grant [W911NF-14-1-0359]
- Scientific Discovery through Advanced Computing (SciDAC) program - U.S. Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences [W911NF-14-1-0359]
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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 Lambda-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 pi-electrons.
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