Perturbational treatment of spin-orbit coupling for generally applicable high-level multi-reference methods.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Spin-orbit coupling is crucial for understanding molecular properties.
• Accurate treatment of spin-orbit coupling requires high-level computational methods.
• Existing methods have limitations in consistency and scalability.

Purpose of the Study:

• To implement an efficient perturbational treatment of spin-orbit coupling.
• To extend the existing two-component (2c) multi-reference configuration interaction singles and doubles (MRCISD) method.
• To provide a consistent and scalable approach for spin-orbit coupling calculations.

Main Methods:

• Implementation of quasi-degenerate perturbation theory (QDPT) model space techniques.
• Utilizing large-scale scalar relativistic MRCISD wavefunctions or LRT-MRAQCC solutions.
• Comparison with fully variational spin-orbit MRCISD calculations.

Main Results:

• The new QDPT approach provides a consistent, size-consistent, and size-extensive treatment of spin-orbit coupling.
• Validation using potential energy surfaces of acrolein and its analogs shows good accuracy.
• Approximate analytic gradients are available for structure optimization and dynamics.

Conclusions:

• The developed method offers an efficient and accurate way to include spin-orbit coupling in high-level quantum chemistry.
• This advancement is beneficial for molecular structure optimization and ab initio molecular dynamics.
• The approach extends the capabilities of the Columbus quantum chemistry package.