Equation-of-motion coupled-cluster methods for doubly ionized and doubly electron-attached states with single, double, and triple substitutions: Theory, implementation, and benchmarks

We present new and computationally efficient implementation of the equation-of-motion (EOM) coupled-cluster methods for doubly ionized (DIP) and doubly electron-attached (DEA) states including single, double, and triple substitutions. In particular, EOM operators include up to 4-hole-2-particle substitutions in EOM-DIP-CCSDT and up to 4-particle-2-holes substitutions in EOM-DEA-CCSDT; both treatments include up to 3-hole-3-particle substitutions in the CC part. These methods have been implemente