The dynamic dielectric constant of an inhomogeneous polar liquid: direct approach from simulation

We report a new method of calculating the dynamic dielectric constant of a polar fluid using molecular dynamics simulation and the first such results for an inhomogeneous dielectric. This technique does not involve measuring the time dependent dipole moment correlation function during the simulation. Rather we measure the response (to an external field) of the polarization and of the electric (essentially Maxwell) field due to the dielectric, inside the liquid. This method is particularly appropriate for inhomogeneous dielectrics. The method is used with computer simulations of a inhomogeneous Stockmayer fluid confined within a hard-walled, spherical cavity. Measurements of the polarization and electric field for subvolumes of the liquid are used to calculate a scalar, dynamic dielectric constant as a function of radius for these systems which display mild microscopic density inhomogeneties.