  We propose a first principle computation of the equilibrium thermodynamics of
simple fragile glasses starting from the two body interatomic potential. A
replica formulation translates this problem into that of a gas of interacting
molecules, each molecule being built of m atoms, and having a gyration radius
(related to the cage size) which vanishes at zero temperature. We use a small
cage expansion, valid at low temperatures, which allows to compute the cage
size, the specific heat (which follows the Dulong and Petit law), and the
configurational entropy.
