On the computer simulation of highly polar fluids using large systems

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Abstract
The determination of the dielectric properties of polar liquids by computer simulation has, in the past, presented both conceptual and computational difficulties. Many of the conceptual problems have now been at least partially resolved, yet the accurate calculation of the dielectric response for a highly polar liquid remains a major computational task. The usual means of obtaining the static dielectric constant, ϵ, is through the fluctuations in the total dipole moment of the system. In this paper we describe an alternate approach which relies upon the long-range asymptotic behaviour of the dipole-dipole correlations in order to determine ϵ. It requires that a rather large simulation cell be employed, in the present case samples of 4000 particles. Molecular dynamics simulations have been performed for a highly polar fluid composed of dipolar soft spheres in which the dipole-dipole interactions have been evaluated using the Ewald summation technique. Results for the static dielectric constant are reported and compared with previous calculations. The microscopic structure is examined in detail with particular attention being paid to the effects of boundary conditions and numerical implementation. We also consider whether the current understanding of these systems can in fact account for the behaviour observed.