Semiclassical Nonadiabatic\nMolecular Dynamics Using\nLinearized Pair-Density Functional Theory

Nonadiabatic molecular dynamics is an effective method\nfor modeling\nnonradiative decay in electronically excited molecules. Its accuracy\ndepends strongly on the quality of the potential energy surfaces,\nand its affordability for long direct-dynamic simulations with adequate\nensemble averaging depends strongly on the cost of the required electronic\nstructure calculations. Linearized pair-density functional theory\n(L-PDFT) is a recently developed post-self-consistent-field multireference\nmethod that can model potential energy surfaces with an accuracy similar\nto expensive multireference perturbation theories but at a computational\ncost similar to the underlying multiconfiguration self-consistent\nfield method. Here, we integrate the SHARC dynamics and PySCF electronic structure code to utilize L-PDFT for electronically\nnonadiabatic calculations and use the combined programs to study the\nphotoisomerization reaction of <i>cis</i>-azomethane. We\nshow that L-PDFT is able to successfully simulate the photoisomerization\nwithout crashes, and it yields results similar to the more expensive\nextended multistate complete active space second-order perturbation\ntheory. This shows that L-PDFT can model internal conversion, and\nit demonstrates its promise for broader photodynamics applications.