Abstract: Diffusion and phase transition are important elements of basic physics teaching at the undergraduate level. In this paper, we study the diffusion and phase transition of water molecules under an external uniform electric field based on molecular dynamics simulations for bulk water system. In the case of smaller electric field, water molecules exhibit significant angular jump reorientation motions, and the frequency of the rotation shows a non-monotonic increasing-decreasing behavior with the electric field. This anomalous electric field dependence of angular jump reorientation is strongly correlated with the non-monotonicity of the diffusion coefficient of water molecules with electric field. The liquid-solid phase transition of the bulk water system, i.e., electrofreezing phenomenon, was reproduced at stronger electric fields, and the layered stacking pattern of the two ice phases was observed. The direction of this layered stacking pattern is consistent with the direction of the electric field. The molecular simulations provide new insights into the molecular mechanisms of water diffusion and phase transition at the microscopic level, and can be used as a teaching example for students to develop research interests and research practice skills.

Key words: electrostatic field, diffusion, electrofreezing, water, molecular dynamics