A simulation study of the decay of the pair correlation function in simplefluids

Monte Carlo simulations are used to investigate the asymptotic decay of the total pairwise correlation function h(r) for some model fluids. We determi ne the poles of the Fourier transform (h) over cap(q) from the direct corre lation function c(r). The leading poles determine the ultimate, r -->infini ty, decay of h(r). For the truncated and shifted Lennard-Jones fluid we cal culate the Fisher-Widom (disorder) line in the temperature-density (T,rho) plane where the ultimate decay of rh(r) crosses over from monotonic (expone ntial) to exponentially damped oscillatory decay. This line lies close to t hat obtained in an earlier integral-equation [hypernetted chain-soft core m ean spherical approximation (HMSA)] study. For states on the monotonic side of the disorder line, h(r) has a finite number of oscillations and we dete rmine the boundaries which mark regions in the (T,rho) plane where h(r) has a given number of zeros using a random-phase approximation for c(r). In th e case of the hard-sphere fluid, the ultimate decay of h(r) is oscillatory for all densities and we find that simulation results for the period and (e xponential) decay length of the oscillations are in good overall agreement with those of Percus-Yevick theory, although there is some indication that systematic differences develop for high-density states rho*greater than or equal to 0.85. (C) 2000 American Institute of Physics. [S0021-9606(00)51003 -4].