Density Response Function and Dynamical Behavior of Liquid

Abstract

The elementary excitation in a simple classical liquid is discussed theoretically. The density response function G(k, z) is derived from the generalized Langevin equation derived by Mori. The time correlation of forces is assumed to decay exponentially in the time of order τ, which is the Maxwell relaxation time and assumed to be independent of wave number. The pole of the density response function is calculated numerically for liquid argon at 84°K. The dispersion relation obtained shows a rather good agreement with the data, and has a solid-like form. The relaxation time which gives the best agreement with experiments is τ=0.65×10⁻¹³s. The damping of the mode becomes rather large for the smaller wave number region near the first maximum of the structure factor.