Implementation of quantum-classical mapping approaches for nonadiabatic molecular dynamics in the PySurf package

Quantum-classical methods for nonadiabatic molecular dynamics, based on the Mayer-Miller-Stock-Thoss mapping, are implemented in the open source computer package PySurf. This complements the implementation of surface hopping approaches performed in previous works, and leads to a unified code that allows nonadiabatic dynamics simulations using various mapping approaches (Ehrenfest dynamics, the linearized semiclassical initial value representation, the Poisson-bracket mapping equation, the “unity” approach for the indentity operator, and the spin mapping method) as well as different flavours of surface hopping (fewest-switches, Landau-Zener, and a mapping-inspired scheme). Furthermore, a plugin is developed to provide diabatic vibronic models in a sum-of-products form. This opens the way to the benchmark of different types of quantum-classical propagators on different models, against exact quantum dynamical simulations performed, e.g., by the multiconfigurational time- dependent Hartree method. Illustrative calculations, performed using the whole set of available propagators, are presented for different harmonic and anharmonic two-state models, exhibiting various degrees of correlation between vibrational modes.