Molecular Dynamics Simulations of Hydrophobic Solutes in Liquid Water

The hydrophobic e ect of small apolar solutes is studied by molecular dynamic (MD) simulations. Interactions between two solutes can be described by the potential of mean force (PMF). The general feature of the PMF between two solutes in water is a potential barrier separating a stable contact con guration and a meta-stable solventseparated con guration. Interestingly, compared with classical MD simulation results, a recent study using quantum mechanical MD simulations found a less pronounced potential barrier and a more stable contact potential minimum. We suggest the former is due to the use of hard-core repulsive potentials in MD simulations, while the latter may result from di erent hydrogen bond network characteristics and the strength of intermolecular interactions between water and solutes. We examined the premise by carrying out classical MD simulations using di erent functional forms of short-range intermolecular repulsive forces. We also did a more in-depth study of hydrogen-bond network distribution in liquid water to characterize solvation shell structures around hydrophobic solutes. The results elucidate the origin of di erences in the PMF between classical forceelds based MD and ab initio MD.