Molecular dynamics study on water evaporation/condensation parameters

An improved two-boundary interphase method was used to evaluate the microscopic condensation coefficient of water and energetic characteristics of water molecules crossing the liquid-vapour interphase from molecular dynamics simulation. The spontaneous evaporation mass flux was obtained from water evaporation into virtual vacuum simulations and was used to calibrate the interphase boundary planes positions for evaporation, condensation and reflection event counting method in liquid-vapour phase equilibria simulations. Our revised microscopic condensation coefficient values are significantly greater than previously published values by Tsuruta and Nagayama (J Phys Chem B 10:1736-1743, 2004), what is consequence of the different methods used for event counting in the interphase. Also, the microscopic condensation coefficient for water is an increasing function of the surface-normal component of translational kinetic energy of the impinging molecules, while the simulation average condensation coefficient, i.e. the macroscopic condensation coefficient, is decreasing function of liquid phase temperature. The analysis of reflected molecules shows that the surface-normal component of translational kinetic energy of reflected molecules after reflection is independent of the components value before reflection. Furthermore, the proposed reflection temperature, which is related to the average value of the surface-normal component of translational kinetic energy of reflected molecules, is significantly lower than the system temperature and is linear function of liquid phase temperature. Finally, a shift of the velocity distribution of reflected molecules was revealed for water.