Ions at the ice/vapor interface

We present Molecular Dynamics simulations of ice growth from a supercooled ionic water solution with explicit ice/vapor and water/vapor interfaces. Starting from a highly asymmetric initial state, the system evolves by freezing water on one side and melting ice on the other side to reach a final symmetric configuration after 30 ns. A strong tendency to the formation of cubic ice is observed. The ions are excluded from the ice and confined to the quasi-liquid layers on both interfaces. The mobility of the ions strongly depends on the thickness of the liquid layer. In a thick liquid layer the ions display free diffusion while in a thin quasi-liquid layer the ions move by an ice surface hopping mechanism.