MOLECULAR-DYNAMICS SIMULATIONS OF WATER IN A SPHERICAL CAVITY

The structure and dynamical properties of water confined to a single smooth spherical cavity as well as a three-dimensional simple cubic array of replica cavities (with cavity diameter equal to the lattice constant) have been studied using molecular dynamics (MD) simulations at 298 K. The water molecules are represented by a simple point charge (SPC) model with flexible intramolecular interactions. The interaction between the water molecules and the spherical cavity surface is modeled as a 9-3 Lennard-Jones potential. This potential has a well depth of about 0.025 eV. Molecular dynamics simulations demonstrate that water in spherical cavities with diameters of about 27 Angstrom has a much smaller dielectric constant (similar to 5) than the bulk system (similar to 80). The surfaces induce a structural ordering of about two to three molecular layers of water at the surface in which the molecular dipoles tend to lie parallel to the surface tangent. Confinement in a spherical cavity has some broadening effect on the spectra of the water molecule as compared to bulk water.