# WavePacket: A Matlab package for numerical quantum dynamics. III: Quantum-classical simulations and surface hopping trajectories

## TL;DR

WavePacket 6.0.2 is a MATLAB package that enables classical, quantum-classical, and quantum simulations of molecular dynamics, incorporating surface hopping algorithms to model non-adiabatic transitions, with extensive documentation and examples.

## Contribution

This work introduces a fully object-oriented MATLAB version of WavePacket that unifies classical and quantum simulations with advanced surface hopping algorithms.

## Key findings

- Implemented surface hopping algorithms including Tully's and Landau-Zener methods.
- Allows simulations on equal footing for classical, quantum, and mixed systems.
- Provides extensive documentation and demonstration examples.

## Abstract

WavePacket is an open-source program package for numerical simulations in quantum dynamics. Building on the previous Part I [Comp. Phys. Comm. 213, 223-234 (2017)] and Part II [Comp. Phys. Comm. 228, 229-244 (2018)] which dealt with quantum dynamics of closed and open systems, respectively, the present Part III adds fully classical and mixed quantum-classical propagations to WavePacket. In those simulations classical phase-space densities are sampled by trajectories which follow (diabatic or adiabatic) potential energy surfaces. In the vicinity of (genuine or avoided) intersections of those surfaces trajectories may switch between surfaces. To model these transitions, two classes of stochastic algorithms have been implemented: (1) J. C. Tully's fewest switches surface hopping and (2) Landau-Zener based single switch surface hopping. The latter one offers the advantage of being based on adiabatic energy gaps only, thus not requiring non-adiabatic coupling information any more. The present work describes the MATLAB version of WavePacket 6.0.2 which is essentially an object-oriented rewrite of previous versions, allowing to perform fully classical, quantum-classical and quantum-mechanical simulations on an equal footing, i.e., for the same physical system described by the same WavePacket input. The software package is hosted and further developed at the Sourceforge platform, where also extensive Wiki-documentation as well as numerous worked-out demonstration examples with animated graphics are available.