Triplet correlations in the Lennard-Jones fluid

Abstract

The thermodynamics and the configuration space structure of the Lennard-Jones fluid are studied using a first-principles integral equation theory previously employed to compare calculated and computer simulated pair and triplet correlation functions for a model of liquid sodium. The modified Yvon–Born–Green integral equation is solved by a new application of the quasilinearization (Newton–Raphson) method, which is found to be much more efficient and more stable than a simple iterative (Picard) method. For particular thermodynamic states, predicted values of the pressure and internal energy are compared with the predictions derived from other integral equation theories, semiempirical perturbation theories, and computer simulations. Information contained in the triplet correlation function is revealed graphically as a function both of distance and of angle. The isothermal density derivative of the pair correlation function is calculated and is found to differ measurably from the result obtained using the superposition approximation for the triplet correlation function. An experimental test of higher order superposition approximations is suggested.