Molecular Dynamics Simulation Of Monolayer Confined Ice-Water Phase Equilibrium And Dielectric Properties Study

Confined water became a recent hot topic in water science due to its extremely abundant structural phase behavior.However,there exist few studies focused on the coexistence of two or more confined water phases and their related properties.We present a methodology for studying the coexistences of two confined phases of water,based on equilibrium molecular-dynamics(MD)simulations.The methodology is applied to the coexistence of the monolayer ice and water(described with a simple water model)confined in the 0.65nm size pore under a lateral pressure of 5000bar,yielding a direct determination of the melting point and extensive atomic-scale characterization for the mono-molecular layer containing the confined ice-water coexistence line.The rough structural type and the capillary fluctuation of the line,the microscopic mechanism of the solid-liquid structural transition along the line,as well as the transport of the point defect in the solid side of the line are identified directly from the MD trajectories.Various profiles of different thermodynamic properties across the coexistence line illustrate the unique features for the in-plane coexistence of the monolayer confined ice-water system,e.g.,the unexpected large width of the crystal-melt transition region,and the compression state along the solid-liquid phase coexistence line.We also developed constant potential method adapted for MD,as the confined wall is the electrode.We also calculated the dielectric constant and capacitance according to the fluctuation of quantity of electricity on the electrodes.And then we try to find the corresponding relation between the energy storage and the structure of confined water molecules.