Charge Transfer with a Spin. I: A Generalized CASSCF Framework for Investigating Charge Transfer in the Presence of Spin-Orbit Coupling

TL;DR

This paper introduces a generalized CASSCF framework that models charge transfer with spin-orbit coupling, enabling accurate and efficient analysis of systems with unpaired electrons and complex spin interactions.

Contribution

It extends the eDSC/hDSC method to include spin-orbit coupling effects using complex spinor orbitals and multiple electronic configurations.

Findings

Achieves smooth potential energy surfaces across various SOC strengths

Provides rapid SCF convergence in systems with spin-orbit coupling

Effectively models charge transfer in systems with odd electrons

Abstract

We present a generalized extension of the recently developed electron/hole-transfer Dynamically-weighted State-Averaged Constrained CASSCF (eDSC/hDSC) method to model charge transfer in the presence of spin-orbit coupling (SOC) for systems containing an odd number of electrons. Our approach incorporates complex-valued spinor orbitals and incorporates four electronic configurations in describing ground-excited state curve crossings between Kramers-restricted doublet states. The method achieves smooth potential energy surfaces and rapid self-consistent field (SCF) convergence across a wide range of spin-orbit coupling strengths, providing an efficient framework for investigating charge transfer processes in the presence of nontrivial spin degrees of freedom.