Coupled-Cluster Valence-Bond Singles and Doubles (CCVB-SD) for Strongly Correlated Systems
CCVB is a computationally efficient approximation of the more expensive spin-coupled valence bond (SCVB) model. It handles molecules with multiple electron pairs localized in the same region, where both inter-pair and intra-pair correlations are strong. CCVB is designed to deal with multiple bond-breaking problems.
CCVB-SD successfully combines the advantages of CCVB and restricted CCSD. It describes valence correlation correctly even near multiple bond dissociation. It is spin-pure, size-extensive, and also more black-box than CCVB as its energy is invariant under rotations in occupied and virtual orbital spaces.
The block-tensor based implementation of CCVB-SD enables large-scale applications, such as calculating acene oligomers correlating up to 318 electrons in 318 orbitals.
Applications include reaction mechanisms involving strongly correlated transition states such as pericyclic reactions.
Correlation energy error with respect to DMRG per acene unit in n-acene of different CC methods
Correlation-energy recovery for various methods in the dissociation of N\(_2\), STO-3G basis