Automated Active Space Selection with CASCI Dipole Moments

Multireference calculations are well-suited for describing properties of highly correlated systems. In order to realize the full potential of multireference methods, it is necessary to judiciously choose the active space. It is possible to do this manually, but an automatic procedure for selecting the active space can benefit high-throughput applications and is not susceptible to human error. We previously developed two protocols, GDM-AS and EDM-AS, where the dipole moment calculated at the complete active space self-consistent field (CASSCF) level of theory is used to select the active space, and demonstrated the e↵ectiveness of these protocols when the chosen active spaces are used to find low-lying excitation energies for molecules with non-zero dipole moments. In this work, we demonstrate that using complete active sapce configuration interaction (CASCI) dipole moments, with the orbitals from the second-order Møller-Plesset perturbation theory, instead of CASSCF dipole moments in our dipole moment 1 active space selection (DM-AS) protocols can significantly improve the e ciency of active space selection compared to our previous methods while maintaining reasonable complete active space second-order perturbation theory (CASPT2) and complete active space pair-density functional theory (CAS-PDFT) vertical excitation energy. We also present new protocols designed for charge transfer states.