Two-component relativistic coupled-cluster methods using mean-field spin-orbit integrals.

Area of Science:

• Quantum Chemistry
• Computational Physics
• Spectroscopy

Background:

• Coupled-cluster (CC) methods are essential for accurate electronic structure calculations.
• Spin-orbit (SO) effects are crucial for heavy elements but computationally demanding.
• Existing methods face computational bottlenecks with large molecular orbital integral files.

Purpose of the Study:

• To develop a novel, efficient implementation of the two-component spin-orbit coupled-cluster singles and doubles (SO-CCSD) and SO-CCSD(T) methods.
• To address the computational bottleneck in calculating the particle-particle ladder term.
• To accelerate the evaluation of electron correlation in relativistic quantum chemistry.

Main Methods:

• Implementation of an atomic-orbital-based algorithm for the particle-particle ladder term in SO-CCSD(T).
• Utilizing the spin-free nature of the Coulomb interaction for computational acceleration.
• Performing benchmark calculations using mean-field SO integrals.

Main Results:

• The new SO-CCSD(T) formulation accelerates the particle-particle ladder term evaluation by approximately a factor of 4.
• Computational bottlenecks associated with large molecular-orbital integral files are removed.
• Accurate calculations of spin-orbit splittings for the thallium atom and diatomic radicals were achieved.

Conclusions:

• The developed atomic-orbital-based SO-CCSD(T) method offers a significant computational speedup.
• This novel implementation provides a more efficient route for accurate relativistic electronic structure calculations.
• The method enables reliable prediction of properties influenced by spin-orbit coupling.