Molecular-dynamics simulation of evaporation of a liquid

The molecular-dynamics method is used to investigate high-temperature evaporation of a simple liquid. The interaction of the atoms is described by a Lenard-Jones 6–12 potential. The simulation shows that fluctuations of the binding energy in the surface layer play an important role in evaporation, thanks to which a significant contribution to the evaporated flux comes from atoms whose kinetic energy is of the same order of magnitude as the mean thermal energy. Such a mechanism of evaporation differs substantially from the traditional one [Ya. I. Frenkel’, Kinetic Theory of Liquids (Clarendon Press, Oxford, 1946)] based on the assumption that only those particles evaporate that have energies of the order of the binding energy, i.e., much larger than the mean thermal energy. The structure of the transitional layer between the bulk gas and liquid phases is investigated. Potential energy fluctuations and pairwise correlation functions in the bulk phases and transitional layer are calculated. The velocity distribution function of the atoms for evaporation into vacuum is found.