The nature of the glass transition and the excess low-energy density of vibrational states in glasses

It is shown that the excess low-energy (2-10 meV) density of vibrational states (LEDOS) in glasses leads to an increase of the mean-square atomic displacements (R2) in comparison with the case of crystalline counterparts. The estimations show that due to the excess LEDOS (R2) at the glass temperature, Tg in glass is the same as in its crystalline counterpart at the melting point Tm. The relation between Tg and Tm is expressed through the parameters of the excess LEDOS and is shown to be in good agreement with the experimental rule Tm/Tg approximately=3/2. A criterion of glass-forming ability, based on the important role of the excess LEDOS, is formulated.