Dissociation line of tetrahydrofuran hydrates from NPH molecular dynamics simulations

In this work, we study via molecular dynamics simulations the dissociation temperature (T2) of the tetrahydrofuran (THF) hydrate. By employing the direct coexistence technique within the isenthalpic-isobaric (NPH) ensemble, we evaluated the T2 values at 100, 250, 500, and 1000 bar using the TIP4P/Ice water model and a rigid, planar TraPPE-UA force field for THF. This rigid and planar THF model based on the TraPPE-UA force field has demonstrated several times to yield identical results as the original and flexible TraPPE-UA model while significantly reducing the computational cost of the simulations. A key methodological aspect of this work is the transition from the traditional isothermal-isobaric (NPT) ensemble to the NPH ensemble to mitigate the stochastic inaccuracies and high computational costs of the hydrate dissociation temperature determination through the classical NPT + direct coexistence methodology. The dissociation temperatures, T2, obtained in this work at 100, 250, 500, and 1000 bar are 276.7(2), 274.2(2), 270.4(3), and 265.9(1) K, respectively. These results show an excellent agreement with existing experimental data and with NPT molecular dynamics simulation data previously reported in the literature. This study concludes that the NPH ensemble, combined with the direct coexistence technique, provides a robust, accurate, and computationally efficient framework for determining the dissociation boundaries of hydrate systems.