Relativistic core-valence-separated equation-of-motion coupled-cluster singles and doubles method: Efficient...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Relativistic Calculations

Background:

• Accurate calculation of core-excited states is crucial for understanding atomic and molecular properties.
• Relativistic effects become significant for heavy atoms, complicating theoretical treatments.
• Existing methods may lack efficiency or accuracy for core-level spectroscopy involving heavy elements.

Purpose of the Study:

• To report an efficient implementation of the relativistic exact two-component core-valence-separated equation-of-motion coupled-cluster singles and doubles (X2C-CVS-EOM-CCSD) method.
• To enhance the efficiency of calculating core-excited states, particularly for systems with heavy atoms.
• To validate the accuracy of the developed method through benchmark calculations.

Main Methods:

• Implementation of the relativistic exact two-component (X2C) Hamiltonian.
• Application of the core-valence-separated (CVS) approximation within the equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) framework.
• Explicit exclusion of pure valence excitations in the excited-state eigenvalue equations.

Main Results:

• The developed X2C-CVS-EOM-CCSD method demonstrates significant efficiency improvements for core-excited state calculations.
• Benchmark calculations incorporating relativistic, correlation, and basis-set effects yield highly accurate results.
• The method accurately predicts properties of core ionized and excited states involving heavy atoms.

Conclusions:

• The efficient X2C-CVS-EOM-CCSD implementation is a valuable tool for studying core-level phenomena in heavy elements.
• This method offers a computationally feasible approach to achieve high accuracy in relativistic core-excited state calculations.
• The findings advance the capability to model and interpret spectroscopic data for heavy-atom systems.