OVERSCREENING IN A POLAR LIQUID AS A RESULT OF COUPLING BETWEEN POLARIZATION AND DENSITY-FLUCTUATIONS

Static nonlocal dielectric response of a polar liquid with linearly co upled polarization and density fluctuations is studied. We use a simpl e quadratic Landau-Ginzburg Hamiltonian to show that the symmetry of i nteraction between density and vectorial polarization might lead to a striking enhancement of the polarizability at a certain finite wavelen gth. A similar effect in water has been obtained in recent computer si mulations in accordance with neutron diffraction data and predicted by molecular theories. Here, we suggest that the coupling between densit y and polarization fluctuations might be one of the sources of this be haviour and discuss the conditions for its realization. A closed-form expression is derived for the wave-vector (k-) dependent response func tion and compared with computer simulation and diffraction data. The e xpression may be used as a simple analytical framework for describing dielectric screening in polar liquids. Implications of the resonance s hape of the response function in k-space are studied for the interioni c mean force potential and for the reorganization energy of electron e xchange reactions between two ions. Copyright (C) 1996 Elsevier Scienc e Ltd.