Restricted open-shell time-dependent density functional theory with perturbative spin-orbit coupling.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Molecular Spectroscopy

Background:

• Studying electronically excited states of open-shell molecules often requires spin eigenfunctions.
• Spin-orbit coupling (SOC) is crucial for excited states in molecules with heavy elements.

Purpose of the Study:

• To implement and assess a ROKS-TDA-SOC method for studying electronically excited states.
• To enable calculation of transition dipole moments for full spectrum simulation.

Main Methods:

• Restricted open-shell Kohn-Sham (ROKS) time-dependent density functional theory.
• Inclusion of spin-orbit coupling (SOC) perturbatively.
• Tamm-Dancoff approximation (TDA) to mitigate numerical instabilities.

Main Results:

• The ROKS-TDA-SOC method was successfully implemented and validated.
• The method allows for the calculation of transition dipole moments.
• Accurate electronic excited states were obtained for molecules with heavy elements.

Conclusions:

• The ROKS-TDA-SOC formalism provides a clear and user-friendly approach.
• This method is suitable for moderate-sized open-shell molecules containing heavy elements.
• Enables efficient and accurate electronic excited state calculations.