Equation-of-motion coupled-cluster theory for double electron attachment with spin-orbit coupling

Area of Science:

• Quantum Chemistry
• Computational Physics

Background:

• Accurate prediction of electronic properties in atoms and molecules is crucial for understanding chemical phenomena.
• Spin-orbit coupling (SOC) significantly influences electronic structures, especially in heavier elements.

Purpose of the Study:

• To implement and assess the equation-of-motion coupled-cluster (EOM-CC) method for double electron attachment (DEA) including spin-orbit coupling (SOC) at the singles and doubles (CCSD) level.
• To investigate the performance of the EOM-DEA-CCSD method with SOC for calculating atomic and molecular properties.

Main Methods:

• Developed the EOM-DEA-CCSD method incorporating SOC within a post-Hartree-Fock framework.
• Utilized two-particle and three-particle one-hole excitations in the DEA operator.
• Employed symmetry (time-reversal and spatial) to optimize computational efficiency.

Main Results:

• The EOM-DEA-CCSD method with SOC accurately calculates double ionization potentials (DIPs), excitation energies (EEs), and SOC splittings for atomic systems.
• For molecules like GaH, InH, and TlH, the method underestimates bond lengths significantly, despite reasonable EEs.
• Calculated SOC splittings for the 3Σ- state in molecules were found to be too small.

Conclusions:

• The EOM-DEA-CCSD method with SOC is a reliable tool for studying SOC effects in atoms.
• Further methodological development is required to improve the accuracy of EOM-DEA-CCSD with SOC for molecular systems.