Generalized Valence Bond-Based Block-Correlated Coupled Cluster Theory with up to Five-Pair Correlation for Accurate Static Correlation of Strongly Correlated Systems.

Generalized valence bond-based block-correlated coupled cluster theory with up to five-pair correlation (GVB-BCCC5) has been presented for the first time to describe the electronic structures of strongly correlated systems with singlet ground states. Several efficient techniques have been employed to make GVB-BCCC5 calculations practical for strongly correlated systems. We then apply this method to investigate various systems, including potential energy surfaces of a hydrogen cuboid lattice and a phosphorus cluster (P4); relative energies of two isomers for C8 and V2H2; and the bond dissociation energy in a metal-oxide compound, FeO3. All calculations show that GVB-BCCC5 can provide nearly the exact static correlation energy as the density matrix renormalization group method (based on the same GVB orbitals). This work demonstrates the potential applications of the GVB-BCCC5 method in the accurate description of many strongly correlated systems.