Quantum and classical molecular dynamics simulations of hydrophobic hydration structure around small solutes

We present a combination of classical and first principles molecular dynamics simulations of hydrophobic hydration structure. Our results show that water molecules surrounding two small hydrophobic solutes are oriented in a similar fashion, and that the driving force for this orientation is the water-water interaction rather than the water-solute interaction. In contrast, the spatial distribution of water around the hydrophobic Solute is strongly influenced by the solute, and the driving force for the observed distribution is largely a steric effect. In addition to the size and structure of the solute, we find that the spatial distribution of water is sensitive to pressure. Using quantum simulations as a benchmark for classical potentials, we evaluate the accuracy of several empirical based models in predicting detailed information regarding the structure of water around small hydrophobic solutes. Our results demonstrate that the radial and spatial distribution of water molecules around different solutes obtained classically and quantum mechanically agree rather well, indicating that classical potentials are well suited for examining these properties related to hydrophobic hydration structure. However. we do find that properties such as the angular distribution of water and hydrogen bond ring statistics agree to a lesser extent and depend strongly on the classical potential employed.