Closed-shell coupled-cluster theory with spin-orbit coupling.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Relativistic Calculations

Background:

• Accurate theoretical predictions for heavy elements are crucial.
• Relativistic effects and spin-orbit coupling significantly impact properties of heavier elements.
• Existing relativistic coupled-cluster methods can be computationally prohibitive.

Purpose of the Study:

• To develop and implement an efficient two-component coupled-cluster (CC) approach for heavy element compounds.
• To incorporate spin-orbit coupling within a post-Hartree-Fock treatment.
• To assess the computational cost and accuracy of the new method.

Main Methods:

• A two-component closed-shell coupled-cluster (CC) method was developed.
• Relativistic effective core potentials and spin-orbit coupling were used.
• The method was implemented at the CC singles and doubles (CCSD) and CCSD(T) levels.

Main Results:

• The two-component CCSD method shows good agreement with CCSD including spin-orbit coupling at the HF-SCF level for bond lengths and harmonic frequencies.
• The CCSD(T) approach maintains high accuracy for 5p- and 6p-block elements.
• Computational cost is significantly reduced (10-15 times nonrelativistic) compared to fully relativistic methods.

Conclusions:

• The proposed two-component CC method provides a computationally efficient and accurate way to study heavy element compounds.
• The method balances accuracy and computational feasibility, particularly for 5p- and 6p-block elements.
• Further investigation may be needed for precise predictions in 7p-block elements due to increased relativistic effects.