EOMIP-CCSD for Ground and Excited States Energies of Open-Shell Systems with Spin-Orbital Coupling

A novel two-component Equation-Of-Motion CCSD method for Ionization-Potential (EOMIP) based on a previously developed CC method with spin-orbital coupling (SOC)^[1-4] included in post-SCF part based on CCSD is implemented in the CFOUR program package^[5]. This approach could be use to calculate both ground and some excited states energies for open-shell systems with SOC. The EOMIP-CC method is computationally more efficient than methods that include SOC in SCF part^[6,7] and free from spin contaminant due to the closed-shell nature of reference states. SOC in the present approach is introduced either in the CC part or in the EOMIP part. The later implementation is particularly efficient since the computational effort for the EOMIP part is much smaller than that of the CCSD calculation without SOC. This approach has been used to calculate some open-shell systems. The splitting value of lowest ²P term for Kr⁺, Xe⁺, Rn⁺, Br, I and At, as well as the splitting value of lowest ²D term for Zn⁺, Cd⁺, Hg⁺, Cu, Ag, and Au. Meanwhile, the ionization energy contributed from s²p⁶ to s²p⁵ for Kr, Xe, Rn and the ionization energy contributed from d¹⁰s² to d⁹s² for Zn, Cd, Hg are calculated. Taking I₂⁺ as a typical molecule, the equilibrium bond length and harmonic frequency for five lowest state of ²Π_g,3/2, ²Π_g,1/2, ²Π_u,3/2, ²Π_u,1/2 and  ²∑_g⁺ are also calculated. The computational results show that the method with SOC included in EOMIP can provide reliable results for atoms and molecules containing even sixth row elements.

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[4] Z. Y. Tu, F. Wang and J. Gauss, unpublished

[5] http://slater.chemie.uni-mainz.de/cfour/

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