Thermodynamics of Solids Including Anharmonicity Through Quasiparticle Theory

30 April 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


The quasiharmonic approximation (QHA) in combination with density-functional theory is the main computational method used to calculate thermodynamic properties under arbitrary temperature and pressure conditions. QHA can predict thermodynamic phase diagrams, elastic properties, and thermal conductivities, all of which are important in various fields of knowledge. The main drawback of QHA is that it makes spurious predictions for the volume and other properties in the high temperature limit due to its approximate treatment of anharmonicity. In this work, we propose a simple extension to QHA that fixes this problem. Our approach is based on four ingredients: i) the calculation of the n-th order force constants using randomly displaced configurations and regularized regression, ii) the calculation of temperature-dependent effective harmonic frequencies with self-consistent harmonic approximation (SCHA), iii) Allen's quasiparticle (QP) theory, which allows the calculation of the anharmonic entropy from the effective frequencies, and iv) a simple Debye-like numerical model that enables the calculation of all other thermodynamic properties from the QP entropies. The proposed method is conceptually simple, with a computational complexity similar to QHA, and allows incorporating anharmonic effects to any order. The predictions of the new method coincide with QHA in the low-temperature limit and eliminate the QHA blowout at high temperature, recovering the experimentally observed behavior of all thermodynamic properties tested. The performance of our new method is demonstrated by calculating the thermodynamic properties of geologically relevant minerals MgO and CaO. We expect this new method to be an important tool in geochemistry and materials discovery.


Computational Thermodynamics
Quasiharmonic approximation
Quasiparticle theory

Supplementary materials

Supporting Information: Thermodynamics of Solids Including Anharmonicity Using Quasiparticle Theory
Supporting figures and tables for the main paper.


Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.