Extending the generalized Chaplygin gas model by using
  geometrothermodynamics
  We use the formalism of geometrothermodynamics (GTD) to derive fundamental
thermodynamic equations that are used to construct general relativistic
cosmological models. In particular, we show that the simplest possible
fundamental equation, which corresponds in GTD to a system with no internal
thermodynamic interaction, describes the different fluids of the standard model
of cosmology. In addition, a particular fundamental equation with internal
thermodynamic interaction is shown to generate a new cosmological model that
correctly describes the dark sector of the Universe and contains as a special
case the generalized Chaplygin gas model.
