MOLECULAR-DYNAMICS SIMULATIONS OF WATER IN A SPHERICAL CAVITY

The structure and dynamical properties of water confined to a single s mooth spherical cavity as well as a three-dimensional simple cubic arr ay of replica cavities (with cavity diameter equal to the lattice cons tant) have been studied using molecular dynamics (MD) simulations at 2 98 K. The water molecules are represented by a simple point charge (SP C) model with flexible intramolecular interactions. The interaction be tween the water molecules and the spherical cavity surface is modeled as a 9-3 Lennard-Jones potential. This potential has a well depth of a bout 0.025 eV. Molecular dynamics simulations demonstrate that water i n spherical cavities with diameters of about 27 Angstrom has a much sm aller dielectric constant (similar to 5) than the bulk system (similar to 80). The surfaces induce a structural ordering of about two to thr ee molecular layers of water at the surface in which the molecular dip oles tend to lie parallel to the surface tangent. Confinement in a sph erical cavity has some broadening effect on the spectra of the water m olecule as compared to bulk water.