Journal of Chemical Physics, Vol.115, No.22, 10500-10508, 2001
Molecular dynamics simulation study of the properties of doubly occupied N-2 clathrate hydrates
We have performed molecular dynamics calculations to obtain a number of properties of a doubly occupied structure II N-2 clathrate hydrate, in particular to study its behavior under higher pressures. The calculated neutron diffraction pattern is in agreement with the experimental result. The effect of the presence of the filling of the small cages and of the large cages (in either single or double occupancy) on the calculated pattern is demonstrated and discussed. The calculated Raman spectra show that the average vibrational frequency of the N-2 molecules decreases in going from the singly occupied small cages to the doubly occupied large cages and then to the singly occupied large cages, respectively. The frequency distributions are explained in terms of radial distribution functions. When applying large pressures at low temperatures, a clathrate-amorphous transition occurs for a partially doubly occupied clathrate. The transition occurs at about the same pressure as for single occupations, but the densification is larger for the latter. In both cases, the transition is reversible.