Classical and quantum molecular dynamics simulations of condensed aqueous systems

Abstract

In this thesis we have used molecular dynamics techniques to investigate the behavior and properties of water in condensed phases at the microscopic level. We have considered three different aqueous systems, studying the equilibrium properties for two of them and the relaxation from non-equilibrium states towards the equilibrium for the third one. On the one hand, we have address the solvation of negatively charged species in water clusters of various sizes. We have employed our own code (capable of performing classical and path integral molecular dynamics simulations at finite temperature) to compute equilibrium properties of water clusters anions and halide ion water clusters. We have explicitly included nuclear quantum effects on the water dynamics, showing that such effects are non-negligible from low temperatures to room conditions. We have focused on the calculation of structural and energetic properties and observed the appearance of distinct solvation motifs of the different charged species in the water clusters. On the other hand, motivated by the controversial macroscopic Mpemba effect, we have explored the non-equilibrium properties of bulk water, which has contributed to attain a better understanding at the molecular level of how condensed systems approach thermodynamic equilibrium. We have analyzed the evolution of the kinetic energy components from initial states breaking the equilibrium partition of the kinetic energy among different modes. Doing so, we have observed the existence of a Mpemba-like microscopic effect in both liquid and solid water, and qualitatively related such effect with the equilibrium autocorrelation functions of the kinetic energy components