Pair and singlet diffusion in a Lennard-Jones liquid

Abstract

Inspired by the experimental work of Richter et al. [1], we have investigated the dynamic behaviour of pairs of particles of a Lennard-Jones liquid for four different thermodynamic states. The short and long time behaviour of dynamic correlation functions of pairs are studied and directly compared with that of single particle correlation functions. Only those relating to singlet and pair diffusion are treated.

A list of the correlation functions considered in this work is presented in the table of the Appendix.

The main results are the following:

	(i)the mean square displacement of pairs of particles departs only slightly from that of single particles (doubled);
	(ii)for long times, the mean square displacement of pairs is significantly reduced when pairs from only the first coordination shell are considered;
	(iii)in the short time region the mean square displacment of pairs resembles that of single atoms, however that of pairs being initially closer than the mean separation of particles in the liquid exhibits a small tendency to lie above the doubled one of single particles.

Our results, obtained by extensive molecular dynamics (MD) calculations, are in quantitative disagreement with results generated by other authors [3, 4], and the findings of Posch et al. [6] could not be confirmed in detail by our work.