Can the AMOEBA forcefield be used for high pressure simulations? The extreme case of methane and water.

We have performed classical molecular dynamics simulations using the fully polarizable Atomic Multipole Optimized Energetics for Biomolecular Applications (AMOEBA) forcefield implemented within the Tinker package to determine whether a more adequate treatment of electrostatics is sufficient to correctly describe the mixing of methane with water under high pressure conditions. We found a significant difference between the ability of AMOEBA and other classical, computationally cheaper forcefields, such as TIP3P, simple point charge-extended, TIP4P, and optimized potentials for liquid simulations-all atom. While the latter models fail to detect any effect of pressure on the miscibility of methane in water, AMOEBA qualitatively captures the experimental observation of the increased solubility of methane in water with pressure. At higher temperatures, the solubility of water in methane also increases; this seems to be associated with the breakdown of the fourfold hydrogen-bonded water network structure: bonding in water is weaker, so the energy cost of solution is lowered.