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

ABSTRACT

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 s¹, p³, σ¹ or π² 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 ³Σ₁⁻ states for high spin state of π² configuration, while the ground state is the ³Σ₀⁻ state. When removing an electron from the high spin state of p³ configuration, only the ³P₂ state can be reached. The open-shell EOM-IP-CCSD approach with SOC was employed in calculating IPs of some open-shell atoms with s¹ configuration, diatomic molecules with π² configuration and SOC splitting of the ionised π¹ state, as well as IPs of VA atoms with p³ 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.

KEYWORDS:

• EOM-CC
• spin-orbit coupling
• open-shell reference
• ionised state

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

We thank the National Nature Science Foundation of China [grant number 21703020], [grant number 21473116] for financial support.