Abstract
A new method implementing molecular dynamics (MD) simulations for calculating the reference properties of simple gas hydrates has been proposed. The guest molecules affect interaction between adjacent water molecules distorting the hydrate lattice, which requires diverse values of reference properties for different gas hydrates. We performed simulations to validate the experimental data for determining , the chemical potential difference between water and theoretical empty cavity at the reference state, for structure II type gas hydrates. Simulations have also been used to observe the variation of the hydrate unit cell volume with temperature. All simulations were performed using TIP4P water molecules at the reference temperature and pressure conditions. The values were close to the experimental values obtained by the Lee-Holder model, considering lattice distortion.
Highlights
Gas hydrates are crystalline solids formed when water forms a complex lattice with gases which occupy the interstices of the hydrogen bonded water molecules [1,2,3,4]
Various calculations have been performed over the years to establish the reference properties of gas hydrates through molecular dynamics (MD) simulation techniques
From the equilibrium data obtained from MD simulations, the volume of the unit cell is plotted for different temperatures
Summary
Gas hydrates are crystalline solids formed when water forms a complex lattice with gases which occupy the interstices of the hydrogen bonded water molecules [1,2,3,4]. The first equilibrium model for gas hydrate was developed by van der Waals and Platteeuw [5] based on statistical thermodynamics and was generalized by Parrish and Prausnitz [3] to form the basis of all the thermodynamic models even today These models were further extended by Holder et al [4] by considering the energy changes due to the restriction of guest molecule movement in the hydrate lattice. The purpose is to validate the data on the reference chemical potential difference and the effect of temperature on the Journal of Thermodynamics size of the unit lattice structure To apply this ensemble to a lattice distortion assumption, the lattice size was changed simultaneously at a constant temperature, and the total energy with the pressure was calculated at each condition. The MD calculations will be used to determine the reference chemical potential difference and the hydrate unit cell size
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