Incorporating spin-orbit effects into surface hopping dynamics using the diagonal representation: a linear-response...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Photochemistry

Background:

• Understanding excited-state dynamics is crucial for photochemistry and photophysics.
• Spin-orbit coupling significantly influences relaxation pathways in molecules with heavy atoms or specific electronic structures.
• Previous methods often simplified or neglected spin-orbit effects, limiting accuracy.

Purpose of the Study:

• To introduce a novel trajectory surface hopping (TSH) method incorporating spin-orbit (SO) effects.
• To investigate the excited-state relaxation mechanisms of 2-thiouracil (2TU) in different environments.
• To validate the method by comparing simulation results with experimental data.

Main Methods:

• Development of a TSH method within the Linear-Response Time-Dependent Density Functional Theory (LR-TDDFT) framework.
• Incorporation of spin-orbit coupling (SOC) using the Breit-Pauli Hamiltonian and Casida's wave functions.
• Simulations of 2TU excited-state relaxation in vacuum and aqueous solutions.

Main Results:

• The primary relaxation pathway for 2TU was identified as S2 → S1 → T.
• Intersystem crossing (ISC) was found to occur at specific molecular geometries and was facilitated by near-degeneracies between singlet and triplet states.
• Simulated internal conversion (IC) and ISC timescales closely matched experimental observations.

Conclusions:

• The developed TSH method with SO effects provides an accurate description of excited-state dynamics.
• The study elucidates the detailed relaxation pathways and ISC mechanisms in 2TU.
• This computational approach offers a valuable tool for studying photophysical processes in similar molecules.