AFLOW-QHA3P: Robust and automated method to compute thermodynamic properties of solids

Abstract

Accelerating the calculations of finite-temperature thermodynamic properties is a major challenge for rational materials design. Reliable methods can be quite expensive, limiting their applicability in autonomous highthroughput workflows. Here, the three-phonon quasiharmonic approximation (QHA) method is introduced, requiring only three phonon calculations to obtain a thorough characterization of the material. Leveraging a Taylor expansion of the phonon frequencies around the equilibrium volume, the method efficiently resolves the volumetric thermal expansion coefficient, specific heat at constant pressure, the enthalpy, and bulk modulus. Results from the standard QHA and experiments corroborate the procedure, and additional comparisons are made with the recently developed self-consistent QHA. The three approaches-three-phonon, standard, and self-consistent QHAs-are all included within the open-source ab initio framework AFLOW, allowing the automated determination of properties with various implementations within the same framework.

High-Throughput Screening of the Thermoelastic Properties of Ultrahigh-Temperature Ceramics

“…The calculation of F vib at a given ϵ is performed using the harmonic approximation, where F vib includes anharmonic effects in the form of strain-dependent phonon frequencies 10 , 23 , 25 where ℏ and k B are the reduced Planck and Boltzmann constants, respectively, and ω j ( q ) is the strain-dependent phonon frequency for the wave vector, q , and phonon branch index j . N q is the total number of wave vectors.…”

“…For metals and narrow band gap systems, the contribution of F elec ( ϵ (δ), T ) to F tot could be important and includes temperature-dependent contribution of the electrons to the internal energy, U elec ( ϵ (δ), T ), and the electronic entropy, S elec ( ϵ (δ), T ) 23 , 25 …”

“… 21 Nevertheless, this approach, based on SC-QHA, 20 overestimates the thermodynamic properties, particularly at high temperatures. 23 Developing a high-throughput framework that predicts temperature-dependent elastic constants and combines accuracy and robustness while also reducing computational costs remains a challenge.…”

“…In this work, we have extended the three-phonon approach, QHA3P method, 23 to calculate temperature-dependent elastic constants combining Taylor expansion with QHA. Following this strategy, Taylor expansion reduces the computational cost, while mechanical and thermodynamical properties at a particular temperature are determined by minimizing free energy.…”

Free Energy of Metals from Quasi-Harmonic Models of Thermal Disorder

“…The first successful applications of Debye-Grüneisen theory to derive thermal properties of metals [1] from the total energies calculated on the basis of density functional theory (DFT) [2,3] were later overshadowed by the great success of quasi-harmonic evaluation of the phonon free energy from DFT-computed phonon spectra [4][5][6][7][8][9]. Furthermore, free energy evaluation by means of thermodynamic integration of ab initio (or classical ab-initio based) molecular dynamical simulation is now often used for describing systems with strong anharmonic effects at high temperatures [10][11][12].…”