The pressure tensor at the planar surface of a liquid

Abstract

The planar surface of a liquid of molecules with truncated Lennard-Jones potentials has been simulated at two temperatures. The normal component of the pressure tensor, p _N(z), is shown to be a constant, independent of the height z. There are many possible definitions of the transverse component, p _T(z); two of these are computed and are shown to differ by small but significant amounts. All definitions of p _T(z) give the same value of the surface tension, but they lead to different values for the apparent height of the surface of tension, that is, the height at which the tension is supposed to act. The difference is about 0·3-0·5 d, where d is the molecular collision diameter, for the two choices of p _T(z) considered here.