A Monte Carlo simulation of the hydrophobic interaction

Abstract

The hydrophobic interaction between two apolar (Lennard–Jones) spheres dissolved in a model of liquid water (ST 2 water) is simulated using the force-bias Monte Carlo technique recently devised by the authors. Importance sampling techniques are devised and used to give a relatively accurate determination of the potential of mean force of the two apolar spheres as a function of their separation. This determination shows that there are two relatively stable configurations for the spheres. In one configuration each member of the pair sits in its own water cage with one water molecule fitting between them. There is a free energy barrier separating this from the other stable configuration which is such that no water molecule sits between the spheres. This conclusion is shown to be quantitatively consistent with the recent semiempirical theory of Pratt and Chandler and is in disagreement with some previous Monte Carlo studies.