A molecular dynamics study of liquid drops

Abstract

We report molecular dynamics studies of small liquid drops (41–2004 molecules) in which the atoms interact with a Lennard-Jones intermolecular potential cutoff at 2.5σ and shifted by the potential at cutoff. We calculate the density profiles ρ(r) and the normal and tangential components of the pressure tensor pN(r) and pT(r), using both the Irving–Kirkwood and Harasima definitions of p. From these functions we calculate the surface thickness, the equimolar radius Re and surface of tension Rs, the surface tension γs referred to Rs, the length δ that appears in Tolman’s equation for γs, the pressure change across the drop, and the densities and pressures of the liquid at the drop center and of the gas. The variation of these properties with both surface curvature and temperature is studied, and the results are used to discuss the validity of Laplace’s equation for the pressure change, Tolman’s equation for the effect of curvature on surface tension, and Kelvin’s equation for the vapor pressure. We also make a qualitative comparison with previous theoretical calculations for drops using density gradient and integral equation theory.