Perturbative spin-orbit couplings for the simulation of extended framework materials.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Materials science

Background:

• Accurate description of photochemical processes, including spin-forbidden transitions like intersystem crossing and phosphorescence, requires accounting for spin-orbit coupling.
• Existing methods may lack efficiency or accuracy in handling these complex quantum mechanical effects.

Purpose of the Study:

• To develop and present an efficient computational implementation for perturbative spin-orbit coupling corrections.
• To integrate this correction into the Tamm-Dancoff approximation of linear-response time-dependent density functional theory (TD-DFT).
• To validate the method using a mixed Gaussian and plane wave framework with spin-orbit coupling corrected pseudopotentials.

Main Methods:

• Implementation of perturbative spin-orbit coupling (SOC) corrections within the Tamm-Dancoff approximation (TDA) of linear-response TD-DFT.
• Utilizing a mixed Gaussian and plane wave (GPW) computational framework.
• Employing SOC-corrected pseudopotentials for efficiency and accuracy.
• Validation against established Density Functional Theory (DFT) and DFT/multi-reference configuration interaction (MRCI) reference data.

Main Results:

• The implementation demonstrates high efficiency for computational timings, including examples with bismuth-containing metal-organic frameworks.
• Validation on small aromatic molecules shows mean errors in excitation energies (0.1–0.6 eV) and spin-orbit coupling matrix elements (1.0–14.4 cm−1) compared to reference methods.
• The method provides accurate results for spin-forbidden processes.

Conclusions:

• The presented efficient implementation of spin-orbit coupling corrections offers a reliable tool for studying photochemical processes in materials.
• This advancement enables more accurate theoretical investigations of systems involving heavy atoms and spin-forbidden transitions.
• The method is validated and ready for application to complex molecular and material systems.