Excitation energies with spin-orbit couplings using equation-of-motion coupled-cluster singles and doubles...

Area of Science:

• Quantum Chemistry
• Computational Physics
• Spectroscopy

Background:

• Calculating excited states with spin-orbit couplings is crucial for understanding molecular and atomic properties.
• Existing methods for handling spin-orbit interactions can be complex and computationally intensive.

Purpose of the Study:

• To develop and implement a novel, simplified method for calculating excited states with spin-orbit couplings.
• To provide a more accessible and general approach compared to traditional methods.

Main Methods:

• Formulation and implementation of a calculation method utilizing left and right eigenvectors of the equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) model.
• Introduction of spin-orbit interactions via the Breit-Pauli Hamiltonian's spin-orbit mean field approximation.
• Evaluation of matrix elements using a diagrammatic scheme based on second-quantization algebra.

Main Results:

• A general and simplified scheme for calculating spin-orbit interactions is presented, outperforming Wigner-Eckart theorem-based rules for configuration state functions.
• Demonstrated the conditions for classifying spin-orbit coupled states according to double group symmetry.
• Developed and implemented an algorithm for classifying target states by irreducible representation of double group symmetry.

Conclusions:

• The developed method accurately predicts spin-orbit splittings for excited states in atoms and molecules, showing good agreement with experimental data.
• The new scheme offers a more straightforward and versatile approach to handling spin-orbit couplings in quantum chemical calculations.