Nonadiabatic Molecular Dynamics by Multiconfiguration Pair-Density Functional Theory

We
present the first implementation of multiconfiguration pair-density
functional theory (MC-PDFT) ab initio molecular dynamics. MC-PDFT
is a multireference electronic structure method that in many cases
has a similar accuracy (or even better accuracy) the complete active
space second-order perturbation theory (CASPT2) at a significantly
lower computational cost. In this study, we introduced MC-PDFT analytical
gradients into the SHARC molecular dynamics program for ab initio,
nonadiabatic molecular dynamics simulations. We verify our implementation
by examining the intersystem crossing dynamics of thioformaldehyde,
and we observe excellent agreement with recent CASPT2 and experimental
findings. Moreover, with MC-PDFT, we could perform dynamics simulations
with the 12 electron in 10 orbitals active space that was computationally
too expensive for direct dynamics with CASPT2.