Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations

A second melting temperature occurs at a temperature T_n+ higher than T_m in glass-forming melts after heating them from their glassy state. The melting entropy is reduced or increased depending on the thermal history and on the presence of antibonds or bonds up to T_n+. Recent MD simulations show full melting at T_n+ = 1.119T_m for Zr, 1.126T_m for Ag, 1.219T_m for Fe and 1.354T_m for Cu. The non-classical homogeneous nucleation model applied to liquid elements is based on the increase of the Lindemann coefficient with the heating rate. The glass transition at T_g and the nucleation temperatures T_nG of glacial phases are successfully predicted below and above T_m. The glass transition temperature T_g increases with the heating rate up to T_n+. Melting and crystallization of glacial phases occur with entropy and enthalpy reductions. A universal law relating T_n+ and T_nG around T_m shows that T_nG cannot be higher than 1.293T_m for T_n+= 1.47T_m. The enthalpies and entropies of glacial phases have singular values, corresponding to the increase of percolation thresholds with T_g and T_nG above the Scher and Zallen invariant at various heating and cooling rates. The G-phases are metastable up to T_n+ because the antibonds are broken by homogeneous nucleation of bonds.