Frequency sum rules of correlation functions in dense gases. I. Molecular-dynamics results

Abstract

Molecular-dynamics simulations of dense Lennard-Jones gases at 297 K have been carried out for number density (a) n=0.0138 Å⁻³ and (b) n=0.0106 Å⁻³ to obtain the static pair correlation function g(r) and the second and fourth frequency sum rules of longitudinal and transverse current correlation functions. The results for the fourth frequency sum rule are compared with those obtained using the superposition approximation (SA) for the static triplet correlation function g₃(r→,r→') appearing in the molecular expression of the sum rule. It is found that errors involved due to the use of SA in the calculation of sum rules are not of much significance. The triplet contribution is found to be the largest near the triple point for wave number q < (¾)q₀, where q₀ is the position of the first peak in S(q), and decreases at lower densities.