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

Abstract

The molecular dynamics study based on two-Lennard-Jones (12-6) centres pair potentials, with reduced bond lengths in the range 0·5 ⩽l/σ⩽0[sbreve]d8, and with ε, σ-parameters simulating liquid F₂, Cl₂, Br₂ and CO₂ (14) is extended to time correlation functions. The calculated properties include: translational velocity and force self correlation functions; orientational self-correlation functions <P _1,2(Î . Î(t))>, a cross correlation function for P ₂, angular momentum (J), and torque self-correlation functions. Diffusion constants (D) and rotational relaxation times (τ₁, τ₂, τ _J ) have been evaluated and where possible compared with experimental data (D and τ _J for F₂, τ₂ for Cl₂). Calculations with 108 or 256 molecules are reported for several densities and temperatures for four model liquids. The nature of the one-particle motion is analysed qualitatively in terms of quasi-oscillations and -librations. It is difficult to fit the observed features into the framework of physical models proposed in the literature. The parametrization in terms of memory functions will be reported in a subsequent paper.