On the effect of CH$_4$, C$_2$H$_6$, CO$_2$ Xe, and H$_2$S guest molecules on the stability of sI-hydrate

Currently, hydrates are of considerable interest among researchers, which is due, firstly, to the use of gas hydrates as promising sources of hydrocarbon energy, and secondly, the possibility of using such molecular systems as reservoirs for hydrogen storage. The thermodynamic properties, formation kinetics, and phase diagrams of gas hydrates are well studied, as evidenced by a large number of experimental and theoretical studies. Despite this, questions remain open related to the lack of understanding of the mechanisms of structure formation and stability of molecular complexes of the «guest-host» type. In this work, within the framework of the density functional theory, some aspects of the structural stability of gas hydrates were studied. It is shown that the inclusion of a gas molecule in the hydrate cavity leads to repulsion of the cavity nodes, which indicates the structural stabilization of the hydrate. The binding energies were calculated for gases such as CH$_4$, C$_2$H$_6$, CO$_2$, Xe and H$_2$S placed in small (D-) and large (T-) cavities of clathrate hydrates. It was found that small CH$_4$, Xe, H$_2$S molecules stabilize D-cavities better, while large C$_2$H$_6$ and CO$_2$ molecules stabilize T-cavities of hydrates better. The densities of electronic states for the hydrate with/without the inclusion of a gas molecule are obtained. When a gas molecule is switched on, a shift in the energy of the electronic subsystem of the hydrate was found, which indicates a decrease in the total energy of the system and an increase in its stability.