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A geometric approach to the thermodynamics of the van der Waals system

We investigate the geometric properties of the equilibrium manifold of a thermodynamic system determined by the van der Waals equations of state. We use the formalism of geometrothermodynamics to obtain results that are invariant under Legendre transformations, i. e., independent of the choice of thermodynamic potential. It is shown that the equilibrium manifold is curved with curvature singularities situated at those points where first order phase transitions occur. Moreover, the geodesic equations in the equilibrium manifold are investigated numerically to illustrate the equivalence between geodesic incompleteness and curvature singularities as a criterion to define phase transitions in an invariant manner.