Equation-of-Motion Block-Correlated Coupled Cluster Method with up to Three-Block Correlation for Excited Electronic States of Strongly Correlated Systems

The equation-of-motion generalized valence bond (GVB) based block-correlated coupled cluster approach with up to three-block correlation (termed EOM-GVB-BCCC3) has been implemented to describe low-lying excited states of strongly correlated systems with large active spaces. The computational time of EOM-GVB-BCCC3 scales as the fifth power of the system size. The method is then applied to investigate low-lying excited states in several strongly correlated systems. Our results demonstrate that EOM-GVB-BCCC3 could provide satisfactory results for the excited states with different spin multiplicities as the complete active space configuration interaction or the density matrix renormalization group method. EOM-GVB-BCCC3 shows significant improvement compared to EOM-GVB-BCCC2b proposed previously. This work demonstrates the potential of EOM-GVB-BCCC3 as a promising tool in investigating low-lying excited states of strongly correlated systems with large active spaces.