Molecular dynamics of water, investigation of rigid non polarizable models from structure to dynamics / by Rana Khairallah Nicolas.

Abstract

Molecular dynamics have been excessively used for investigation of liquids. Interest in simulating liquid water started since 1969 with Alder and Wainwright. The field has evolved tremendously since then, many water models have been formulated and a lot of success was achieved. Water models from empirical and semi-empirical to ab-initio are improving with the day, and simulations of bigger systems is becoming possible with the increase of computer power. After investigation of water models in the literature we decided to do our simulations of water using three rigid non-polarizable models the simple charge point SPC, the transferable intermolecular potential 3p TIP3P, and the 4p TIP4P. Structural properties, mainly the radial distribution function for distinctive sites is studied for the three models, and compared with experimental results. Effect of temperature on the radial distribution functions was also investigated from cold to superheated and supercritical water. Pair energy distributions are also studied and analyzed at different temperatures. Analysis of the hydrogen bond from the pair energy distribution is also present. Dynamical properties were also investigated. Diffusion coefficient was measured for the three models using the Einstein formula, at ambient conditions and at different temperatures and densities. Rotational diffusion was also measured and the relaxation times computed for the three models, and compared with experimental data. Finally some analysis was made concerning the hydrogen bond correlation function.