The longitudinal dielectric function, chi(k) = 1 - 1/epsilon(L)(k), Of both polar and nonpolar liquid environments is a key ingredient to modern theories of solvent effects upon charge transfer reactions in solution and solvation dynamics processes in general. In this work, we present a molecular dynamics simulation study of the dielectric function of several molecular liquids ranging from associating (H2O, CH3OH) and nonassociating ((CH3)(2)SO, CH3CN) polar liquids to nondipolar ones (C6H6, CCl4 and CO2) aiming to better understand the relationships between the structure of the chi(k) functions to the charge-charge spatial correlations in each liquid. We show that the characteristic main peak of chi(k), located at some wave vector k*, whose value depends on the liquid, arises from spatial charge density fluctuations of wavelength 2 pi/k* for all liquids considered, with the exception of CO2. Further details about the shape of the chi(k) functions for the simulated liquids are discussed in terms of intra and intermolecular charge-charge correlations. (C) 2000 Elsevier Science B.V. All rights reserved.5054553