GIBBS:: isothermal-isobaric thermodynamics of solids from energy curves using a quasi-harmonic Debye model

Given the energy of a solid (E) as a function of the molecular volume (V), the gibbs program uses a quasi-harmonic Debye model to generate the Debye temperature Theta (V), obtains the non-equilibrium Gibbs function G* (V; p, T), and minimizes G* to derive the thermal equation of state (EOS) V(p, T) and the chemical potential G(p, T) of the corresponding phase. Other macroscopic properties are also derived as a function of p and T from standard thermodynamic relations. The program focuses in obtaining as much thermodynamical information as possible from a minimum set of (E, V) data, making it suitable to analyse the output of costly electronic structure calculations, adding thermal effects at a low computational cost. Any of three analytical EOS widely used in the literature can be fitted to the p - V (p, T) data, giving an alternative set of isothermal bulk moduli and their pressure derivatives that can be fed to the Debye model machinery.