Molecular dynamics of liquids modelled by ‘2-Lennard-Jones’ pair potentials

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Abstract
Mori's continued fraction method has been applied with closure at the second level to the velocity and angular momentum autocorrelation functions (acf) and with closure at the third level to the orientational acfs <Pl(t)>l=1, 2. The acfs were obtained in molecular dynamics simulations of diatomic liquids modelled by 2-Lennard-Jones centres potentials (1,2). Various trial functions used for the closure are tested by regeneration of the acfs. A gaussian function exp (-(t/t 1)2) with t 1 determined by static properties leads to a good reproduction of the initial main lobe but fails at large t if the acf has a negative tail. Two-term trial functions with small, slowly decaying tails reproduce the acfs quite well. It is found that the same trial functions which are used in the closure at second level of angular momentum acf also produce comparably good fits if used in the third level closure of the reorientational acfs.