Computational Mechanics Approach to Water Diffusion

Abstract

This thesis discusses the methods and results of nine molecular dynamic simulation models. The models computationally simulate the evaporation of water into nitrogen. The models are varied by temperature at 25C, 50C, and 75C and by box dimensions, where the y-dimension is increased from 115 angstroms to 330 and 460 angstroms. From the simulation data, diffusivities are calculated and compared between different water isotopes. The two water isotopes studied are those with heavy hydrogen (D\(_{2}\)O) and heavy oxygen H\(_{2}\)\(^{16}\)O. This thesis determines the self-diffusion coefficients of all isotopes in every model from rigorous mean squared displacement analysis of the output trajectories. Validation of the model behaving in accordance to real water is offered through analysis of the equilibration of particular system thermodynamic variables and of comparison of pair correlation functions to published research. The diffusion coefficients are compared to those predicted by the Einstein-Stokes relation, confirmed by published research, and correction factors dependent upon temperature and box dimensions are discussed. This work offers questioning into the universality of correction factors on diffusion coefficients and proposes deviation analysis on model parameters in order to reliably utilize all model results.