Quantum dynamical concertedness: an entangled trajectory molecular dynamics study

We study the dynamics of a model for double proton transfer reaction in order to gain insights into the reaction mechanism. The model potential energy surface exhibits four minima, four rank one saddles and a second rank saddle. Our interest in this model is twofold. First, to establish the extent to which the mechanism can be classified as a dynamically concerted one as a function of total energy. Second, to investigate whether quantum dynamics can significantly alter the notion of dynamical concertedness. The first issue is addressed by a classical dynamical analysis of the so called delay time distributions as a measure of dynamical concertedness, which shows that the fraction of dynamically concerted reactive trajectories exhibits substantial fluctuations even at energies well above that of the rank two saddle energy. For the second question our approach involves using the entangled trajectory molecular dynamics method to compute the quantum analog of the classical delay time distribution. Our results show that one can still use the notion of dynamical concertedness. However, significant deviations due to quantum effects are observed in certain energy and parameter regimes. Such quantum deviations are further characterized by computing the linear entropy of the system, which hints at the possible role of quantum entanglement.