On the Use of Quantum Thermal Bath in Unimolecular Fragmentation Simulation.

In the present work, we have investigated the possibility of using the quantum thermal bath (QTB) method in molecular simulations of unimolecular dissociation processes. Notably, QTB is used in introducing nuclear quantum effects with a computational time, which is basically the same as in Newtonian simulations. At this end, we have considered the model fragmentation of CH4 for which an analytical function is present in the literature. Moreover, based on the same model, a microcanonical algorithm, which monitors the zero-point energy of products and eventually modifies trajectories, was recently proposed. We have thus compared classical and quantum rate constants with these different models. QTB seems to correctly reproduce some quantum features, in particular the difference between classical and quantum activation energies, making it a promising method to study, with molecular simulations, unimolecular fragmentation of much complex systems. The role of a QTB thermostat in rotational degrees of freedom is also analyzed and discussed.