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[Licence| Download | New Version Template] aevq_v2_0.tar.gz(55367 Kbytes)
Manuscript Title: Phasego 2.0: Counting full anharmonic effects from high-temperature phonon density of states
Authors: Zhong-Li Liu
Program title: Phasego2
Catalogue identifier: AEVQ_v2_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 197(2015)341
Programming language: Python (versions 2.4 and later).
Computer: Any computer that can run Python (versions 2.4 and later).
Operating system: Any operating system that can run Python.
RAM: 50 M bytes
Keywords: Anharmonic free energy corrections, Gibbs free energy, Phase diagram, Thermodynamic properties.
Classification: 7.8.

External routines: Numpy [1], Scipy [2], Matplotlib [3]

Does the new version supersede the previous version?: Yes

Nature of problem:
The anharmonic lattice vibrations have more and more contributions to Gibbs free energy when temperature is beyond Debye temperature and goes up to melting temperature. The quasi-harmonic approximation (QHA) only includes part of the anharmonic effects due to the volume variation of frequency. At high temperature, the neglect of phonon-phonon interactions in the QHA will introduce errors and even arrive at wrong conclusions. However, the calculation of the anharmonic free energy from the phonon-phonon interactions is very complicated to perform.

Solution method:
The contribution of phonon-phonon interactions to free energy can be naturally extracted from the high-temperature phonon density of states (DOS). The extraction and inclusion of anharmonic free energy are simplified and automated in the updated version. The thermal properties of materials are then corrected by including full anharmonic effects with respective to the QHA results.

Reasons for new version:
We have improved the package considerably to include full anharmonic contributions of phonon-phonon interactions. The calculations of thermal properties of materials are automated and easy to implement after anharmonic corrections.

Summary of revisions:
  • The anharmonic free energy extraction functionality is added. Now the Gibbs free energy can include full anharmonic effects.
  • The thermal expansion coefficients are deduced by taking into account full anharmonic contributions.
  • The bulk moduli, the heat capacities, the thermal pressures can include and reflect the contributions of phonon-phonon interactions.
  • The Hugoniot pressure-volume-temperature relations, the Grüneisen parameters, and the Debye temperatures are corrected by anharmonic effects.
  • The Polynomial curve fitting of Helmholtz free energy is added.
  • The unit of Gibbs free energy in the output files is changed.
  • A number of bugs have been corrected.

The restrictions are from the high-temperature phonon DOS calculations. The smaller interval of temperatures at which the phonon DOS are calculated will yield more accurate results. The accuracy of the previously calculated phonon DOS also affect that of the final results.

Unusual features:
The Gibbs free energy of phonon-phonon interactions are automatically extracted from the high-temperature phonon DOS. The anharmonic effects of all the thermal properties are automatically corrected.

Additional comments:
The new version of this package can treat the high-temperature phonon density of states data from many methods, including the molecular dynamics (MD) simulations [4], the self-consistent ab initio lattice dynamics (SCAILD) calculations [5], or other simulation methods.

Running time:
The examples provided in the distribution take less than 5 minute to run.

[1] www.numpy.org.
[2] www.scipy.org.
[3] www.matplotlib.org.
[4] O. Hellman, I. A. Abrikosov, and S. I. Simak, Phys. Rev. B, 84 (2011) 180301.
[5] Souvatzis, P. and Eriksson, O. and Katsnelson, M. I. and Rudin, S. P., Phys. Rev. Lett., 100 (2008) 095901.