Configuration Interaction Singles with Spin-Orbit Coupling: Constructing Spin-Adiabatic States and Their Analytical Nuclear Gradients

TL;DR

This paper develops a method to compute spin-adiabatic states and their nuclear gradients within Configuration Interaction Singles theory, enabling efficient modeling of photoexcited processes involving spin-orbit coupling.

Contribution

It introduces a new approach to calculate spin-adiabatic states and gradients within CIS, facilitating surface hopping dynamics with spin-orbit effects in quantum chemistry.

Findings

Implementation within Q-Chem software verified

Additional computational cost is manageable

Preliminary results show practical applicability

Abstract

For future use in modeling photoexcited dynamics and intersystem crossing, we calculate spin-adiabatic states and their analytical nuclear gradients within CIS the- ory. These energies and forces should be immediately useful for surface hopping dynamics, which are natural within an adiabatic framework. The resulting code has been implemented within the Q-Chem software and preliminary results suggest that the additional cost of including SOC within the singles-singles block is not large.