Abstract
Molecular dynamic simulations were carried out for liquid-vapor interface of n-pentane. Interactions among n-pentane molecules are represented by the Lennard-Jones potential function. In this calculation, the Gibbs surface is adopted. To simulate thermodynamic quantities at a liquid-vapor interface, 216 n-pentane molecules were set in a cubic box. At first, the surface energy (U) was calculated, and then surface tension (γ). Surface energy was obtained from the difference between surface potential energy (17 replicas) and bulk potential energy (26 replicas). Surface tension was determined using the equation U=γ-T (dγ/dT).
In this calculation, the condition that γ=0 at critical temperature (470K) is introduced. From values of surface energy and surface tension, surface entropy was obtained. Surface energy was 50.80erg/cm2 and surface tension, 19.13dyn/cm. Deviation in surface tention from the experimental value was ca. 19.8%. Surface entropy was 0.108erg/K cm2.
