Melting dynamics of superheated argon: nucleation and growth.

We investigate the microscopic melting process of a superheated argon solid using molecular dynamics simulations. We characterize the melting dynamics by following the temperature and time evolutions of liquid atoms and demonstrate the formation of a critical liquid nucleus via fluctuations and subsequent growth. The critical liquid nucleus size (about 120 atoms) obtained from our direct simulations is in accord with the prediction of the classical nucleation theory. The dynamic nucleation and growth of liquid also agree with the Johnson-Mehl-Avrami law, and the growth exponent n approximately 3 at the early stage followed by a substantial increase in n thereafter.