Simulating chemical processes from scratch: classical and quantum molecular dynamics


Abstract


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 Schrödinger 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.

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