Coupled-cluster valence bond (CCVB) was introduced a decade ago by two of us (D.W.S and M.H.G), which is size-consistent, polynomial scaling, spin-pure, and capable of breaking multiple bonds simultaneously. However, its lack of orbital-invariance often limits its applicability to systems with an obvious pairing scheme. On the other hand, restricted coupled-cluster singles and doubles (RCCSD) is size-consistent, exact for non-interacting electron pairs, and orbital-invariant, but it catastrophically fails when breaking bonds. Combining CCVB and RCCSD yields another model called coupled-cluster valence-bond singles and doubles (CCVB-SD) which inherits all the desirable properties of both CCVB and RCCSD. CCVB-SD can be considered a simple modification to RCCSD which scales the same as RCCSD and provides a qualitatively correct description to strongly correlated systems. We discuss the production level implementation of CCVB-SD using block-tensors as implemented in Q-Chem. We then discuss its application to polyacenes, a well-known test platform for strong correlations.

Coupled-Cluster Valence Bond Singles and Doubles (CCVB-SD): Block-tensor based implementation and application to polyacenes

253rd National Meeting (2017)

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