Energetics of water proton configurations in gas hydrates: comparison of various water models

The total interaction energies for a large number of water proton configurations in the unit cell of hydrate structure I consisting of 46 molecules are compared for qualitatively different water models, such as SPC/E, TIP4P, TIP5P, TIP 3f and AMOEBA. All calculations were carried out using the TINKER molecular modelling package. The Ewald summation method with metallic tin-foil boundary conditions is used to account for long-range electrostatic interactions. It was established that there is a high correlation between the energies calculated using the five water models (interaction potentials). The average correlation coefficient for all pairs of potentials is equal to 0.91. Analogous calculations were carried out to evaluate the consistency of the different water models with respect to a new property of the ice-like system: the hydrogen-bond-reversal asymmetry. It was established that, for all water models, there is relatively high correlation between the energy differences for proton configurations with opposite direction of all hydrogen bonds. In this case, the average correlation coefficient is 0.77. Data for the TIP4P potential differ noticeably from the others, especially owing to the variation in the total interaction energy. The validity and usefulness of simple discrete models of inter-molecular interactions are discussed.