Simulation of the THF hydrate-water interfacial free energy from computer simulation.

In this work, the tetrahydrofuran (THF) hydrate-water interfacial free energy is determined at 500 bar, at one point of the univariant two-phase coexistence line of the THF hydrate, by molecular dynamics simulation. The mold integration-host methodology, an extension of the original mold integration technique to deal with hydrate-fluid interfaces, is used to calculate the interfacial energy. Water is described using the well-known TIP4P/Ice model, and THF is described using a rigid version of the TraPPE model. We have recently used the combination of these two models to accurately describe the univariant two-phase dissociation line of the THF hydrate in a wide range of pressures from computer simulation [Algaba et al., J. Chem. Phys. 160, 164718 (2024)]. The THF hydrate-water interfacial free energy predicted in this work is compared with the only experimental data available in the literature. The value obtained, 27(2) mJ/m2, is in excellent agreement with the experimental data taken from the literature, 24(8) mJ/m2. To the best of our knowledge, this is the first time that the THF hydrate-water interfacial free energy is predicted from computer simulation. This work confirms that the mold integration technique can be used with confidence to predict the solid-fluid interfaces of complex structures, including hydrates that exhibit sI and sII crystallographic structures.