Gibbs2: A new version of the quasi-harmonic model code. I. Robust treatment of the static data Original Research Article

We describe in this article the techniques developed for the robust treatment of the static energy versus volume theoretical curve in the new version of the quasi-harmonic model code [Comput. Phys. Commun. 158 (2004) 57]. An average of strain polynomials is used to determine, as precisely as the input data allow it, the equilibrium properties and the derivatives of the static curve. The method provides a conservative estimation of the error bars associated to the fitting procedure. We have also developed the techniques required for detecting, and eventually removing, problematic data points and jumps in the curve. The fitting routines are offered as an independent octave package, called AsturFit, with an open source license.