Exchange-correlation and spin-orbit coupling effects in 18-electrons transparent conductors half-Heusler: Ab-initio study

Abstract

The structural and electronic properties of a two non-oxide Transparent Conductors (TC’s), Ir-based halfHeusler XIrSb (X = Ti,Zr) are studied using DFT based on plane waves pseudo potential method. We examined two aspects: (i) the effect of the exchange–correlation (XC) approximation, namely: PBE, PBE+U and meta-GGA SCAN (The strongly constrained and appropriately normed); and (ii) the spin–orbit coupling (SOC) effects of the heavy metals on these compounds. We found that: (i) SCAN, similar to PBE+U, yields larger band gap compared to the PBE corresponding values for both compounds. SCAN gives a band gap about halfway between PBE and experiment or Hybrid-GGA. Similarly to PBE and PBE+U, SCAN shows the semiconducting behavior of the compounds with indirect band gap at the same locations in Brillouin Zone; (ii) spin–orbit coupling causes an important splitting in the valence band maximum (VBM) of order 0.44 eV and 0.58 eV for TiIrSb and ZrIrSb respectively leading to reduction of the band gap. Thus, the heavier is the X atom the larger is the SOC splitting. The VBM is dominated by 𝐽𝑒𝑓𝑓 = 3∕2 state. However, the splitting is almost negligible on the conduction band minimum (CBM). Therefore, SOC is crucial for predicting the band gap and reproducing correctly the electronic structure of these compounds.