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

Area of Science:

• Quantum chemistry
• Computational chemistry
• Spectroscopy

Background:

• Calculating electronically excited states for molecules with multiple unpaired electrons is difficult.
• Heavy-element systems require spin-orbit coupling (SOC) for accurate modeling.
• The complex wave function nature complicates excited state calculations.

Purpose of the Study:

• To enhance the accuracy of calculating excited states in challenging molecular systems.
• To improve the modeling of spin-orbit coupling effects in heavy elements.
• To extend existing quantum chemistry methods for broader applicability.

Main Methods:

• Modified the SOC-corrected restricted open-shell Kohn-Sham (ROKS) time-dependent density functional theory (TD-DFT) approach.
• Utilized the Tamm-Dancoff approximation (TDA).
• Extended the ROKS-TDA-SOC method to include scalar relativistic spin-flip-down states.

Main Results:

• The enhanced ROKS-TDA-SOC method efficiently calculates lowest-lying SOC-split excitation energies.
• Accurate calculations were achieved for molecular systems with heavy elements and multiple unpaired electrons.
• The inclusion of spin-flip-down states improved the description of SOC interactions.

Conclusions:

• The modified ROKS-TDA-SOC method provides an efficient and accurate approach for calculating excited states.
• This method is particularly valuable for heavy-element systems with complex electronic configurations.
• The study advances computational chemistry for challenging molecular systems.