Molecular Dynamics Exploration of Thin Liquid Films on Solid Surfaces. 2. Polyatomic Nonpolar Fluid and Water Films

The methodology used to simulate a monatomic film on a solid metallic surface is extended to polyatomic nonpolar fluids and water. In this extension, the wall potential is calculated in the same manner as for a monatomic fluid since the intermolecular distance is generally much larger than the molecular size. Nonpolar films are simulated in a manner very similar to the monatomic system since no long-ranged Coulombic potentials are present. The water simulation methodology uses a corrected 3-D Ewald summation technique, but this technique limits the number of vapor molecules in the simulation domain such that the system must be equilibrated to a value far from the critical point. As a result, the lack of vapor molecules in the water system does not allow for calculation of the equilibrium saturation pressure via external pressure adjustment, but rather the simulation is run with a fixed external pressure. In this study, a diatomic nitrogen film at T/T _c = 0.55 and three water films (T = 100, 127, and 140°C) were simulated. The resultant calculated bulk liquid density and surface tension compare well with ASHRAE recommended values, and these results are consistent with previous calculations for a monatomic system.

Keywords:

• liquid-solid interaction
• molecular dynamics
• stochastic methods
• water

Access to the Millennium workstation cluster at UC Berkeley for the MD simulation studies is appreciated, and correspondence with Dr. In-Chul Yeh was valuable.