Crystal and electronic structure of BiTeI, AuTeI, and PdTeI compounds: A dispersion-corrected density-functional study

Abstract

Semilocal and dispersion-corrected density-functional calculations have been performed to study the crystal structure, equation of state, and electronic structure of metal tellurohalides with chemical formula MeTeI where Me=Bi, Au, or Pd. A comparative investigation of the results of these calculations is conducted, which reveals the role of van der Waals attraction. It is shown that the prediction of crystal structure of metal tellurohalides is systematically improved thanks to the inclusion of van der Waals dispersion. It is found for BiTeI and AuTeI that the energy versus volume curve is anomalously flat in the vicinity of equilibrium volume and the calculated equation of state has an excessively steep slope in the low-pressure region, which are also fixed in the dispersioncorrected calculations. Analysis based on the computation of the volume and axial compressibilities shows that predicting the anisotropy of BiTeI via the semilocal calculations yields an unrealistic result whereas the results of dispersion-corrected calculations agree with the experimental compressibility data. Our calculations render that BiTeI (AuTeI) is a narrow band gap semiconductor with Rashba-type spin-splitting at the band edges (with an indirect band gap) while PdTeI is a metal with relatively low density of states at the Fermi level. The band gaps of BiTeI and AuTeI obtained via semilocal (dispersion-corrected) calculations are found to be greater (smaller) than the respective experimental values, which is against (in line with) the expected trend. Similarly, the Rashba parameters of BiTeI are bracketed by the respective values obtained via semilocal and dispersion-corrected calculations, e.g., a larger value for the Rashba parameter αR is obtained in association with the reduction of the band gap caused by modification of the crystal structure owing to van der Waals attraction. Excellent agreement with the experimental Rashba parameters is obtained via interpolation of the calculated (semilocal and dispersion-corrected) values.

BiTeI Kristalinde Spin-Yörünge Yarılmasının Gerinim ile Değişimi

“…Değiş-tokuş-ilgileşim fonksiyoneli olarak Perdew-Burke-Ernzerhof (PBE) fonksiyoneli [28] kullanılmıştır. Önceki bir yayınımızda [22] van der Waals dispersiyon etkileşmesinin hesaba katılmasının gerekli olduğu açığa çıkmıştır. Bu nedenle, PBE fonksiyoneline ilaveten yarı-ampirik bir dispersiyon potansiyeli [29] kullanılmıştır.…”

“…BiTeI yarıiletkeninin spin-ayrışmış Rashba bantlarına ait ölçüm [1, [15][16][17] ve hesaplama [18][19][20][21][22][23] sonuçlarını rapor eden çok sayıda yayın çıkmaktadır. Katmanlı bir yapıya sahip olan BiTeI kristalini, ilk-prensip hesaplamaları gerçekleştirerek, incelediğimiz önceki bir yayınımızda [22], BiTeI bant yapısında oluşan Rashba tipi yarılmaların kökeni araştırılmıştır: BiTeI katmanlarının arasındaki bölgelerde içsel bir 2B elektron gazının oluştuğu açığa çıkarılmıştır. Bununla beraber, BiTeI katmanlarının kompozisyonunun birli olması ve bizmut, tellür ve iyot atomlarının elektronegatiflik değerlerinin uygun düşmesi sayesinde, zikredilen içsel 2B elektron gazının maruz kaldığı asimetrik bir içsel elektrik alanın da var olduğu anlaşılmıştır.…”

Pressure dependence of the band-gap energy in BiTeI

“…Ref. 8. In this structure, adjacent (unary) layers formed by Bi, Te, and I atoms stack along the c-axis, and the van der Waals (vdW) gap exists in the vacuum region between the Te and I layers.…”

“…The parameters used for the semiempirical (van der Waals) force field 10 were the same as in Ref. 8. It should be mentioned that although we were inclined to employ a nonempirical van der Waals density functional (in lieu of the semiempirical force field) such as the optB86b-vdW functional, 20 we unfortunately found that the crystal structure of BiTeI was not adequately described by using the optB86b-vdW functional, as discussed in the Appendix.…”

“…Furthermore, strong (weak) SOC leads to a smaller (larger) band gap as well as a greater (smaller) Rashba coupling strength. 8 The decreasing behavior of the band gap, cf. Figs.…”