Effect of density functionals on the vibrational and thermodynamic properties of Fe2VAl and Fe2TiSn compounds

Abstract

First-principles phonon calculations along with Kohn-Sham density functional theory (DFT) is an essential tool to study the lattice dynamics, thermodynamical properties and phase-transitions of materials. The two full-Heusler compounds Fe2VAl and Fe2TiSn are studied for lattice vibration dependent properties using finite displacement method and supercell approach. For the investigation, four density functionals viz., LDA, PBE, PBEsol and meta-GGA SCAN are employed. Using these functionals, phonon dispersion, phonon density of states (DOS), partial density of states (PDOS) thermal propertis and zero-point energy are calculated at equilibrum lattice parameters under harmonic approximation. For the two compounds the Debye temperatures are calculated from the obtained phonon DOS which are ∼660 K and ∼540 K, respectively. The obtained results from different functionals are compared among each other. The overall phonon energy in the dispersion is found to be ∼15 meV higher in Fe2VAl than the Fe2TiSn compounds. For the two compounds PBE is yielding the lowest phonon frequencies while LDA or SCAN functional is giving the highest. The same pattern is observed in phonon DOS plots of two compounds. The zero-point energy calculated is the highest from SCAN (21.04 and 16.95 J) and the lowest from PBE functionals (20.09 and 16.02 J) obeying the same trend as frequency for both compounds. A general prediction of nature of lattice thermal conductivity is made based on the velocities of acoustic phonons which is in agreement with the qualitative behavior of reported experimental thermal conductivity of two compounds. Phonon spectra obtained from PBE and SCAN have similar general features while those from LDA and PBEsol have resembling features for Fe2VAl, while this trend is not observed for the compound Fe2TiSn.

Towards the high-throughput prediction of finite-temperature properties using the quasi-harmonic approximation

“…As for the lattice constants, we find that figures 1 and 2 reveal some clear trends. Across all the spectra PBE predicts the lowest frequencies, while LDA/SCAN predict the highest, which is consistent with calculations on Fe 2 VAl and Fe 2 TiSn [77]. In the Group 1 and 12 oxides the differences between the functionals are most evident in the high-frequency optic branches of the dispersions, whereas the optic modes in the Group 2 oxides appear to be much less sensitive to the exchange-correlation treatment.…”

Thermoelectric properties, efficiency and thermal expansion of ZrNiSn half-Heusler by first-principles calculations

“…The Debye frequency ω D which is a measure of maximum phonon frequency is ∼33 meV in case of ZrNiSn as computed from total DOS. Using the value of ω D , the calculated Debye temperature Θ D for ZrNiSn is ∼382 K. The value of Θ D indicates that all the vibrational modes in ZrNiSn are excited above 382 K. The value of Θ D for ZrNiSn is relatively lower compared to the Θ D of full Heusler compounds studied in our previous work [27,42]. Rogl et al have reported Θ D of 398 K for ZrNiSn compound from sound measurements [43].…”

First-Principles Analysis of the Raman Spectra of 2D Material YbOCl

“…The choice of xc-functional has an impact on the phonon calculation results, which in turn affects the calculated Raman spectrum. ,− It is well known that the PBE functional tends to overestimate lattice parameters and underestimate the phonon frequencies in crystals, while the LDA functional shows the opposite behavior, i.e., it underestimates the lattice parameter and overestimates the phonon frequency . To investigate the impact of xc-functionals on the harmonic Raman spectrum, various xc-functionals with and without vdW dispersion correction (TS functional) were employed in the calculation.…”