Thermally induced transformations of methane hydrate clusters

The article is devoted to a study of the stability and thermally induced structural transformations of methane-containing water clusters in the form of cavities D and T of the sI hydrate structure. The approach followed in this paper is based on previous experience in modelling of empty water polyhedra taking into account a comprehensive list of possible polyhedra, as well as the strong dependence of the stability of water polyhedra on the direction of hydrogen (H-) bonds. In relation to hydrate clusters, the suitability of the discrete model of strong and weak H-bonds (SWEB model) has been proven, which makes it possible to classify configurations according to the total binding energy. The energy within this model is determined by the number of most preferred types of H-bonds. It has been established that a number of structural transitions from one polyhedron to another are accompanied by an increase in the number of the preferred types of hydrogen bonds. The influence of the guest methane molecule on the degree of tetrahedrality of the H-bond network and on the nature of the transition between the solid-like and liquid-like states of clusters has been studied.