Computer simulations of dynamic crossover phenomena in nanoconfined water.

In order to study dynamic crossover phenomena in nanoconfined water we performed a series of molecular dynamics (MD) computer simulations of water clusters adsorbed in zeolites, which are microporous crystalline aluminosilicates containing channels and cavities of nanometric dimensions. We used a sophisticated empirical potential for water, including the full flexibility of the molecule and the correct response to the electric field generated by the cations and by the charged atoms of the aluminosilicate framework. In addition, the full flexibility of the aluminosilicate framework was included in the calculations. Previously reported and new simulations of water confined in a number of different types of zeolites in the temperature range 100-300 K and at various coverage are discussed in connection with the experimental data. Dynamic crossover phenomena are found in all the considered cases, in spite of the different shape and size of the clusters, even when the confinement hinders the formation of tetrahedral hydrogen bonds for water molecules. Hypotheses about the possible dynamic crossover mechanisms are proposed.