Accurate calculation of excited electronic state properties in the condensed phase systems represents the main bottleneck for efficient application of semiclassical nonadiabatic molecular dynamics (NA-MD) methods for investigation of nonadiabatic processes in the condensed phase taking place after photoexcitation. A variational delta self-consistent field (ΔSCF) density functional theory (DFT) based method represents a potential approach to address the aforementioned constraints in addition to perturbative time-dependent density functional theory (TD-DFT). We applied a restricted Kohn-Sham formulation of ΔSCF with constrained and rounded occupation numbers for NA-MD and employed TD-DFT to aid in excited state SCF convergence and provide guess electronic state densities.[1] By utilizing the combined Gaussian and plane waves approach with periodic boundary conditions the method is easily applicable to full atomistic DFT simulations of condensed phase and it can be combined with subsystem density embedding to further expand its capabilities. This enables targeted modeling of specific excited states in the manifold of dense electronic transitions, as usually encountered in condensed phase systems, without compromising any accuracy in the description of the chromophore–environment interaction. We applied it to study the nonradiative deactivation mechanism of photoexcited diimide in water solution, and show the advantages and disadvantages of such a pragmatic new technique for efficient simulation of nonadiabatic processes in the condensed phase.[2] By expanding the excited electronic state density into a linear combination of singly excited ground state determinants, spin-orbit coupling terms can be easily evaluated and the NA-MD expanded with intersystem crossings between singlet and triplet states.

[1] Momir Malis, Sandra Luber, Journal of Chemical Theory and Computation, 2020, 16, 4071-4086

[2] Momir Malis, Sandra Luber, Journal of Chemical Theory and Computation, 2021, 17, 1653-1661