Structure and Forces in Simple Liquid Metals

Abstract

This paper is based on the exact force equation for a classical monatomic liquid with pairwise interactions.

This is handled by expanding the triplet correlation function g ⁽³⁾ in Legendre polynomials to yield

where g(r) is the radial distribution function, ϕ(r) the pair potential, ρ is the number density, while Q ₁ is the l = 1 term in the Legendre polynomial expansion of g ⁽³⁾.

From molecular dynamics data for some simple liquids, we have calculated the left-hand-side of Eq. (i). This has been used to draw some conclusions about the usefulness of the Kirkwood superposition approximation in extracting forces from structure. Used in the right way, the Kirkwood approximation yields a quantitative estimate of the three-body term in the force equation for Na, but is much less useful for argon.