Hydrophobic hydration around a pair of apolar species in water

The structure of ST2 water around a pair of spherical nonpolar (Lennard‐Jones) particles, A1–A2, is studied as a function of pair separation, r, using a force‐bias Monte Carlo technique with importance sampling. The change in the water structure (or equivalently the hydrophobic hydration) is correlated with the potential of mean force, WAA (r), determined in a previous study. It is found that the second minimum in WAA (r) corresponds to a water molecule lying between the two apolar particles. The water always maintains a ’’linear hydrogen bond’’ network and is more ordered in the neighborhood of the two spheres except possibly when they are separated by a distance corresponding to the position of the free energy barrier, that is the maximum in WAA (r).