Energy landscape - a key concept in the dynamics of liquids and glasses

There is a growing belief that the mode coupling theory is the proper microscopic theory for the dynamics of the undercooled liquid above and around a critical temperature T c . In addition, there is some evidence that the system leaves the saddle points of the energy landscape to settle in the valleys at this critical temperature. Finally, there is a microscopic theory for the entropy well below T c (i.e. close to the calorimetric glass transition T g ), of Mézard and Parisi, which allows one to calculate the Kauzmann temperature from the atomic pair potentials. Description of the dynamics of the frozen glass phase is at present limited to phenomenological models. In the spirit of the energy landscape concept, one considers an ensemble of independent asymmetric double-well potentials with a wide distribution of barrier heights and asymmetries (the 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 centres begins to play a role. In a mean-field treatment, the interaction reduces the number of relaxation centres needed to bring the shear modulus down to zero by a factor of three.