Study on the structure and properties of liquids under various environments using molecular dynamics simulations

Abstract

I have studied the structure and properties of liquid state using molecular dynamics simulations method. The major points I have dealt with are structural changes of water induced by an external electric field and the curvature dependence of the surface tension of argon liquid. At first, using molecular dynamics simulations with the rigid TIP4P water model, I have analyzed the structural change of liquid water induced by an external electric field. The temperature was controlled with a Nose-Hoover thermostat. From this simulation study, I found liquid water with the enhanced structural regularity by applying an electric field could be acquired. Through the simulations under various strengths of the electric field, I can see that the threshold for the significant structural change is thought to be between 0.2 and 0.15 V/Å. When the number of six-membered rings is increased by the external electric field, so that water is forced to have structural regularity, I calculate the diffusion coefficients and discover that water I make in the simulations is not solid but still liquid under the electric field. Secondly, I present the first molecular dynamics simulation study of vapor bubbles. Molecular dynamics simulations are carried out to examine the curvature dependence of the surface tension for argon vapor bubble as well as liquid droplet. Using the Irving-Kirkwood pressure tensor, I calculate the surface tension and the surface of tension by two thermodynamic methods. The results for the surface tension of droplet show that the surface tension decreases with decreasing droplet radius. On the other hand, the surface tension of vapor bubble increases with decreasing bubble radius.