Gibbs2: A new version of the quasiharmonic model code. II. Models for solid-state thermodynamics, features and implementation

• Published in: Computer physics communications 2011-10, Vol.182 (10), p.2232-2248
• Main Authors: Otero-de-la-Roza, A., Abbasi-Pérez, David, Luaña, Víctor
• Format: Article
• Language: English
• Subjects: Approximation; Data analysis; Density of states; Discontinuous data; Equations of state in solids; Equilibrium properties of solids; Fittings; FORTRAN; Mathematical models; Running; Thermal effects; Treatment of noisy data; UNIX (operating system); Windows (computer programs)
• ISSN: 0010-4655; 1879-2944
• DOI: 10.1016/j.cpc.2011.05.009

In the second article of the series, we present the Gibbs2 code, a Fortran90 reimplementation of the original Gibbs program [Comput. Phys. Commun. 158 (2004) 57] for the calculation of pressure–temperature dependent thermodynamic properties of solids under the quasiharmonic approximation. We have taken advantage of the detailed analysis carried out in the first paper to implement robust fitting techniques. In addition, new models to introduce temperature effects have been incorporated, from the simple Debye model contained in the original article to a full quasiharmonic model that requires the phonon density of states at each calculated volume. Other interesting novel features include the empirical energy corrections, that rectify systematic errors in the calculation of equilibrium volumes caused by the choice of the exchange-correlation functional, the electronic contributions to the free energy and the automatic computation of phase diagrams. Full documentation in the form of a userʼs guide and a complete set of tests and sample data are provided along with the source code. Program title:Gibbs2 Catalogue identifier: AEJI_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEJI_v1_0.html Program obtainable from: CPC Program Library, Queenʼs University, Belfast, N. Ireland Licensing provisions: GNU General Public License, v3 No. of lines in distributed program, including test data, etc.: 936 087 No. of bytes in distributed program, including test data, etc.: 8 596 671 Distribution format: tar.gz Programming language: Fortran90 Computer: Any running Unix/Linux Operating system: Unix, GNU/Linux Classification: 7.8 External routines: Part of the minpack, pppack and slatec libraries (downloaded from www.netlib.org) are distributed along with the program. Nature of problem: Given the static E(V) curve, and possibly vibrational information such as the phonon density of states, calculate the equilibrium volume and thermodynamic properties of a solid at arbitrary temperatures and pressures in the framework of the quasiharmonic approximation. Additional comments: A detailed analysis concerning the fitting of equations of state has been carried out in the first part of this article, and implemented in the code presented here. Running time: The tests provided only take a few seconds to run. ► Calculation of thermodynamic properties from first principles data. ► Robust fitting of energy versus volume curves using averages of strain polynomials. ► Models for int