Spin-Orbit Couplings for Nonadiabatic Molecular Dynamics at the Delta SCF Level

A procedure for the calculation of spin-orbit coupling (SOC) at the delta self-consistent field (Delta SCF) level of theory is presented. Singlet and triplet excited electronic states obtained with the Delta SCF method are expanded into a linear combination of singly excited Slater determinants composed of ground electronic state Kohn-Sham orbitals. This alleviates the nonorthogonality between excited and ground electronic states and introduces a framework, similar to the auxiliary wave function at the time-dependent density functional theory (TD-DFT) level, for the calculation of observables. The Delta SCF observables of the formaldehyde system were compared to reference TD-DFT values. Our procedure gives all components (energies, gradients, nonadiabatic couplings, and SOC terms) at the Delta SCF level of theory for conducting efficient, full-atomistic nonadiabatic molecular dynamics with intersystem crossing, particularly in condensed phase systems.