Exotic dielectric behavior of polar liquids

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Abstract
We present a report of our analysis of wave vector dependence of the static dielectric function of a dipolar liquid obtained by a microscopic calculation. At low values of the wave vector (k), the longitudinal dielectric function ε(k) increases with k, in contradiction to some assumptions reported in the literature. As the value of k is increased, ε(k) diverges at a critical value kc which depends on the value of the long wavelength static dielectric constant (ε0) of the liquid. The dielectric function is negative for values of k greater than kc. At large values of k, the calculated ε(k) fails to attain the limiting value of unity. We attribute this result to the failure of the point dipole assumption made in the evaluation of the polarization correlation function required by the theory. The behavior of ε(k) for the dipolar liquid is compared with that of one component plasma for which reliable results can be obtained over the full range of wave vectors. For both systems, the stability conditions are fulfilled at all values of k. A plausible explanation of this rather exotic behavior of ε(k) is given.