Equation of motion coupled cluster method for electron attached states with spin–orbit coupling

We report implementation of the equation of motion coupled-cluster method for electron attachment (EOMEA-CC) based on a previously developed CC approach with spin–orbit coupling included in post-Hartree–Fock treatment at the CC singles and doubles level (CCSD). Time-reversal symmetry is exploited by dealing with one partner of a Kramers pair explicitly and determining the other one through time reversal. This EOMEA-CCSD approach has been applied to calculate properties of some open-shell atoms and molecules containing heavy elements and is found to be able to describe SOC effects with reasonable accuracy.