(350c) Hydrate Molecular Structures By Molecular Dynamics Simulations and Thermodynamic Stability Analysis

Hydrates are crystalline structures composed of cages of hydrogen-bonded water molecules in which small molecules may be trapped. The nucleation mechanisms of crystallization are not fully resolved as they cannot be accessed experimentally. There are limited successes for simulation of hydrates. Most species that they form hydrates cannot be modeled  by molecular simulations. Even for these limited  molecules  most of the reported simulations capture some of the basic elements of the full structure. In few reports, formation of crystalline structures is reached by imposing very high pressure, or dynamic changes of temperature, or a preexisting hydrate structure. In a series of nanoscale molecular dynamics simulations of supersaturated water-methane mixtures or other hydrocarbons we use thermodynamic limit of stability and succeed to capture both nucleation and growth of hydrates. In this work the details of the hydrate formation at moderate subcooling is presented. Not only we can observe the formation of hydrates and realistic structure, our simulation time is sometimes 3 orders of magnitude faster than the past work. This work sets the stage for molecular dynamics simulations of hydrates at realistic conditions for practical applications.