The stochastic self-consistent harmonic approximation: calculating vibrational properties of materials with full quantum and anharmonic effects.
anharmonicity
computational methods
first-principles methods
ionic fluctuations
quantum effects
stochastic self-consistent harmonic approximation
Journal
Journal of physics. Condensed matter : an Institute of Physics journal
ISSN: 1361-648X
Titre abrégé: J Phys Condens Matter
Pays: England
ID NLM: 101165248
Informations de publication
Date de publication:
13 Jul 2021
13 Jul 2021
Historique:
received:
09
03
2021
accepted:
28
05
2021
pubmed:
29
5
2021
medline:
29
5
2021
entrez:
28
5
2021
Statut:
epublish
Résumé
The efficient and accurate calculation of how ionic quantum and thermal fluctuations impact the free energy of a crystal, its atomic structure, and phonon spectrum is one of the main challenges of solid state physics, especially when strong anharmonicy invalidates any perturbative approach. To tackle this problem, we present the implementation on a modular Python code of the stochastic self-consistent harmonic approximation (SSCHA) method. This technique rigorously describes the full thermodynamics of crystals accounting for nuclear quantum and thermal anharmonic fluctuations. The approach requires the evaluation of the Born-Oppenheimer energy, as well as its derivatives with respect to ionic positions (forces) and cell parameters (stress tensor) in supercells, which can be provided, for instance, by first principles density-functional-theory codes. The method performs crystal geometry relaxation on the quantum free energy landscape, optimizing the free energy with respect to all degrees of freedom of the crystal structure. It can be used to determine the phase diagram of any crystal at finite temperature. It enables the calculation of phase boundaries for both first-order and second-order phase transitions from the Hessian of the free energy. Finally, the code can also compute the anharmonic phonon spectra, including the phonon linewidths, as well as phonon spectral functions. We review the theoretical framework of the SSCHA and its dynamical extension, making particular emphasis on the physical inter pretation of the variables present in the theory that can enlighten the comparison with any other anharmonic theory. A modular and flexible Python environment is used for the implementation, which allows for a clean interaction with other packages. We briefly present a toy-model calculation to illustrate the potential of the code. Several applications of the method in superconducting hydrides, charge-density-wave materials, and thermoelectric compounds are also reviewed.
Identifiants
pubmed: 34049302
doi: 10.1088/1361-648X/ac066b
doi:
Types de publication
Journal Article
Review
Langues
eng
Sous-ensembles de citation
IM
Informations de copyright
Creative Commons Attribution license.