Simulating chemical processes from scratch: classical and quantum molecular dynamics

Chemistry is a quantitative science in which rate processes play a major role. Not only they determine the time-scale for molecular transformations, they also determine the preferential outcome of complex reaction networks, such as those occurring in biological environments, at the solid-gas interface of a catalytic system, in the earth atmosphere and in the interstellar medium. Despite this, the quantitative study of the rate of chemical reactions is largely a young field of research. This is due to both inherent difficulties in obtaining accurate potential energy functions for dynamical simulations and in following the dynamical processes themselves. In this work we summarize the efforts we have made in recent years in this exciting field. We start showing how accurate quantum chemistry methods can be used to map the interaction potentials governing the dynamics in small, yet complex systems where the common Born-Oppenheimer approximation ceases to be valid. Then, we show how classical molecular dynamics may be applied in predicting the behaviour of atoms/molecules impinging on a surface, an issue of paramount importance in catalysis. Quantum molecular dynamics is mandatory when inherently quantum systems are involved, and we show how present-day techniques allow to solve exactly the time-dependent Schroedinger equation in simple molecular systems. We finally show our very recent results in describing interaction and energy dissipation of simple quantum systems coupled to a heat reservoir. These represent the first real-time quantum dynamical simulations in very large systems.