Configurational entropy and collective modes in normal and supercooled liquids

Soft vibrational modes have been used to explain anomalous thermal properti es of glasses above 1 K. The soft-potential model consists of a collection of double-well potentials that are distorted by a linear term representing local stress in the liquid. Double- well modes contribute to the configurat ional entropy of the system. Based on the Adam-Gibbs theory of entropically driven relaxation in liquids, we show that the presence of stress drives t he transition from Arrhenius to Zwanzig-Bassler temperature dependence of r elaxation times. At some temperature below the glass transition, the energy scale is dominated by local stress, and soft modes are described by single wells only. I:It follows that the configurational entropy vanishes, in agr eement with the "Kauzmann paradox." We discuss a possible: connection betwe en soft vibrational modes and ultrafast processes that dominate liquid dyna mics near the glass transition. [S1063-651X(99)12108-1].