Energy Landscape -a Key Concept in the Dynamics of Glass Formers

There is a growing belief that the mode coupling theory is the proper microscopic theory for the dynamics of the undercooled liquid above a critical temperature T c. In addition, there is some evidence that the system leaves the saddlepoints of the energy landscape to settle in the valleys at this critical temperature. Finally, there is a microscopic theory for the entropy at the calorimetric glass transition T g by Mézard and Parisi, which allows to calculate the Kauzmann temperature from the atomic pair potentials. Thus two thirds of the glass transition problem seem to be solved; the fragility, i.e. the energy landscape dynamics between T c and the calorimetric glass transition T g remains the only unsolved problem. A possible way to approach this problem is to consider an ensemble of independent asymmetric double-well potentials with a wide distribution of barrier heights and asymmetries (ADWP or Gilroy-Phillips model). The model gives an excellent description of the relaxation of glasses up to about T g /4. Above this temperature, the interaction between different relaxation centers begins to play a role. One can show that the interaction reduces the number of relaxation centers needed to bring the shear modulus down to zero by a factor of three. Energy landscape-a key concept in the dynamics of glass formers 2