Equation-of-motion coupled-cluster method for ionised states with spin-orbit coupling using open-shell reference wavefunction

The equation-of-motion coupled-cluster method for ionised states at the singles and doubles level (EOM-IP-CCSD) with spin-orbit coupling (SOC) included in post-Hartree-Fock (HF) steps is extended to spatially non-degenerate open-shell systems such as high spin states of s(1), p(3), sigma(1) or (2) configuration in this work. Pseudopotentials are employed to treat relativistic effects and spin-unrestricted scalar relativistic HF determinant is adopted as reference in calculations. Symmetry is not exploited in the implementation since both time-reversal and spatial symmetry is broken due to SOC. IPs with the EOM-IP-CCSD approach are those from the (3)sigma(-)(1) states for high spin state of (2) configuration, while the ground state is the (3)sigma(-)(0) state. When removing an electron from the high spin state of p(3) configuration, only the P-3(2) state can be reached. The open-shell EOM-IP-CCSD approach with SOC was employed in calculating IPs of some open-shell atoms with s(1) configuration, diatomic molecules with (2) configuration and SOC splitting of the ionised (1) state, as well as IPs of VA atoms with p(3) configuration. Our results demonstrate that this approach can be applied to ionised states of spatially non-degenerate open-shell states containing heavy elements with reasonable accuracy.