Multiconfiguration pair-density functional theory (MC-PDFT) is a multireference electronic structure method that predicts reaction energies and excitation energies that are of comparable accuracy (or even better accuracy) than complete active space second-order perturbation theory (CASPT2), and yet MC-PDFT has the advantage of being significantly less computationally expensive than CASPT2 for treating strongly correlated systems. In recent years, analytical nuclear gradients have been developed for single-state and multistate MC-PDFT, and this presentation will describe pushing MC-PDFT beyond single-point calculations to model dynamic properties. The beginning of this talk will focus on the first application of MC-PDFT nonadiabatic molecular dynamics to investigate the S<sub>1</sub> to T<sub>2</sub> transition of thioformaldehyde. This work showed MC-PDFT to be a promising method for nonadiabatic molecular dynamics simulations by providing results comparable to multistate CASPT2 at a more affordable cost. The second part of this talk will focus on the development of nonadiabatic couplings for compressed multistate pair-density functional theory (CMS-PDFT), a multistate extension of MC-PDFT that has analytical nuclear gradients. This will allow us to model internal conversion processes with the topologically correct potential energy surfaces around conical intersections. Taken together, the two parts of this presentation will describe the progress towards making MC-PDFT a method that can be applied to understand photodynamic properties in systems that were previously considered too large for accurate multireference calculations.

Multiconfiguration pair-density functional theory beyond single-point calculations

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