Molecular dynamics simulations of binary structure H hydrogen and methyl-tert-butylether clathrate hydrates

Abstract

Binary structure H (sH) hydrogen and methyl-tert-butylether (MTBE) clathrate hydrates are studied with molecular dynamics simulations. Simulations on a 3 x 3 x 3 sH unit cell with up to 4.7 mass % hydrogen gas are run at pressures of 100 bars and 2 kbars at 100 and 273 K. For the small and medium cages of the sH unit cell, H2 guest molecule occupancies of 0, 1 (single occupancy), and 2 (double occupancy) are considered with the MTBE molecule occupying all of the large cages. An increase of the small and medium cage occupancies from 1 to 2 leads to a jump in the unit cell volume and configurational energy. Calculations are also set up with 13, 23, and 89 of the MTBE molecules in the large cages replaced by sets of three to six H2 molecules, and the effects on the configurational energy and volume of the simulation cell are determined. As MTBE molecules are replaced with sets of H2 guests in the large cages, the configurational energy of the unit cell increases. At the lower temperature, the energy and volume of the clathrate are not sensitive to the number of hydrogen guests in the large cages; however, at higher temperatures the repulsions among the H2 guest molecules in the large cages cause an increase in the system energy and volume.

Monte Carlo Calculations of the Free Energy of Binary SII Hydrogen Clathrate Hydrates for Identifying Efficient Promoter Molecules

“…The aim of this work is to compare efficiencies of various promoter molecules, therefore we obtained geometries, point charges and force field parameters for each promoter following the same recipe. For promoter interactions GAAF-like 32 model potentials are used, similar to those used in the simulation studies of binary 7 clathrate hydrates 25,26,33 . To represent the electrostatic interactions, partial charges are placed on atomic sites.…”

The thermodynamic and ground state properties of the TIP4P water octamer

“…The TIP4P model is a four-site model for water, therefore one would anticipate significant differences in the thermodynamic properties when comparing with the SPC model for water. Given the difficulties encountered while trying to resolve which hydrogen bonding arrangement is favored energetically for the real water octamer by potential models, it is highly likely that future simulations of more complicated systems, such as clathrates for example, [54][55][56][57][58][59][60][61][62] will require reproducibility tests of quantitative results with two or more models. The classical heat capacity of the octamer has proved to be sensitive to the details of the potential energy surface.…”

“…As such, the water octamer serves as an ideal testbed for theories and numerical methods for the simulation of more complex systems that contain water. [54][55][56][57][58][59][60][61][62] Despite the relatively small size of the water octamer, its global optimization has proved to be challenging. Stillinger and David 3 report the first optimized structure of the octamer using a model that includes polarization corrections.…”

Monte Carlo study of sII and sH argon hydrates with multiple occupancy of cages

“…Additional studies that consider the case of multiple occupancy include, among others, the experimental [24][25][26] and the theoretical [27][28][29] works for nitrogen, the experimental [30,31] and the theoretical [32][33][34][35][36][37] works for hydrogen, and the theoretical work for carbon dioxide [38].…”