Theoretical and computer-simulation study of the density fluctuations in liquid water

Abstract

A theoretical and molecular dynamics analysis of hydrogen and oxygen density correlation functions in liquid water is presented with the aim of clarifying the present experimental situation. In the theoretical study, besides the ordinary sound mode, a high-frequency ‘‘optical-like’’ collective mode is found to propagate through the hydrogen atoms. The dispersion relation of the two modes is discussed. Computer-simulation results for the partial intermediate scattering functions are reported and confirm the theoretical predictions. The direct comparison of the theoretical predictions and the computer-simulation results with the experimental findings suggests an interpretation of the nature of the two modes. Finally the collective character of the propagating modes is pointed out by comparing the self-part of the scattering function with the total one.