Exact two-component equation-of-motion coupled-cluster singles and doubles method using atomic mean-field spin-orbit...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Spin-orbit coupling (SO) effects are crucial for understanding electronic structures, especially in heavy elements.
• Equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) is a powerful method for calculating excited states.
• Previous SO-EOM-CCSD methods faced computational bottlenecks due to large data requirements and processing demands.

Purpose of the Study:

• To develop a more computationally efficient semi-atomic-orbital-based algorithm for SO-EOM-CCSD.
• To reduce the computational cost associated with the similarity-transformed Hamiltonian in SO-EOM-CCSD calculations.
• To validate the new algorithm by applying it to systems with extended virtual spaces and heavy elements.

Main Methods:

• A novel semi-atomic-orbital-based algorithm for two-component SO-EOM-CCSD was developed.
• The algorithm optimizes the evaluation and storage of Hamiltonian elements, reducing computational bottlenecks.
• The exact two-component Hamiltonian with atomic mean-field SO integrals (X2CAMF) was employed for calculations.

Main Results:

• The new algorithm reduces storage requirements by an order of magnitude and computational operations by 3-4 times.
• Calculations on the triiodide ion (I3-) validated the algorithm's ability to handle extended virtual spaces.
• Ground and excited states of As2, Sb2, and Bi2 were computed, with results supporting a revised assignment of Bi2 photoelectron spectra.

Conclusions:

• The developed SO-EOM-CCSD algorithm offers significant computational advantages.
• The method is capable of accurately describing electronic structures in systems with heavy elements.
• The study provides new insights into the electronic spectroscopy of Bi2, challenging previous assignments.