  Molecular dynamic simulations were performed for ice Ih with a free surface.
The simulations were carried out at several temperatures and each run lasted
more than 7ns. At high temperatures the ice melts. It is demonstrated that the
melting process starts at the surface and propagates to the bulk of the ice
block. Already at the temperatures below the melting point, we observe a thin
liquid layer at the ice surface, but the block of ice remains stable along the
run. As soon as the temperature reaches the melting point the entire ice block
melts. Our results demonstrate that, unlike in the case of conventional
simulations in the NpT ensemble, overheating of the ice Ih with a free surface
does not occur. That allows to estimate the melting point of ice at zero
pressure. We applied the method to the following models of water: SPC/E, TIP4P,
TIP4P/Ew, TIP4P/Ice and TIP4P/2005, and found good agreement between the
melting temperatures obtained by this procedure and the values obtained either
from free energy calculations or from direct simulations of the ice/water
interface.
