Equation-of-Motion Block-Correlated Coupled Cluster Method for Excited Electronic States of Strongly Correlated Systems

Abstract

An equation-of-motion block-correlated coupled cluster method based on the generalized valence bond wave function (EOM-GVB-BCCC) is proposed to describe low-lying excited states for strongly correlated systems. The EOM-GVB-BCCC2b method with up to two-pair correlation has been implemented and tested for a few strongly correlated systems. For a water hexamer with stretched O–H bonds, which is beyond the capability of the CASSCF method, EOM-GVB-BCCC2b provides very close results as the density matrix renormalization group (DMRG). For four conjugated diradical species with triplet ground states, we found that their vertical S–T gaps from EOM-GVB-BCCC2b are also quite consistent with the DMRG results. This new method is expected to be a promising theoretical tool for describing the low-lying excited states of strongly correlated systems with large active spaces.

Geminal-Based Strategies for Modeling Large Building Blocks of Organic Electronic Materials

“…Most promising geminal theories for excited-state calculations are based on the extended random phase approximation , and the EOM formalism. − Although most EOM-based methods yield size-intensive energies, the corresponding properties derived from transition density matrices are not. Yet, the computations of transition dipole moments from EOM could be more computationally impractical due to the need to compute both left and right eigenvectors.…”