# On-the-fly CASPT2 surface hopping dynamics

## TL;DR

This paper introduces a new computational program enabling on-the-fly nonadiabatic surface hopping simulations using XMS-CASPT2 theory, applicable to sizable molecular systems in gas and condensed phases.

## Contribution

The authors developed and integrated an efficient XMS-CASPT2-based surface hopping simulation tool with existing dynamics packages, allowing accurate nonadiabatic dynamics for large systems.

## Key findings

- Successfully simulated 9H-adenine and GFP chromophore in water.
- Demonstrated the program's applicability to sizable molecular systems.
- Made the program publicly available in the bagel package.

## Abstract

We report the development of programs for on-the-fly surface hopping dynamics simulations in the gas and condensed phases on the potential energy surfaces computed by multistate multireference perturbation theory (XMS-CASPT2) with full internal contraction. On-the-fly nonadiabatic dynamics simulations are made possible by improving the algorithm for XMS-CASPT2 nuclear energy gradient and derivative coupling evaluation. The program is interfaced to a surface hopping dynamics program, Newton-X, and a classical molecular dynamics package, tinker, to realize such simulations. On-the-fly XMS-CASPT2 surface-hopping dynamics simulations of 9H-adenine and an anionic GFP model chromophore (para-hydroxybenzilideneimidazolin-5-one) in water are presented to demonstrate the applicability of our program to sizable systems. Our program is implemented in the bagel package, which is publicly available under the GNU General Public License.