Electronic and optical properties of bismuth oxyhalides from ab initio calculations

So far, semiconductors materials have gained huge attention from researchers because of their superior electrocatalytic activity and employment in different areas. The bismuth oxyhalides BiOXs bulks have great electrocatalytic properties and stability. Astonishingly, few of them have synthesized and there is still a lack of theoretical and experimental data on their bandgap energy, which limits the chance of producing new physical properties. Using density functional theory and beyond with GW and GW BSE approaches, we investigate the electronic and optical properties such as absorption coefficient of bismuth oxyhalides BiOXs (where, X = F, Cl, Br, and I). Our results show that the GW bandgap nature of BiOF is direct, whereas the GW bandgaps of BiOCl, BiOBr, and BiOI are indirect, which is a range from 2.33 eV (BiOI) to 4.04 eV (BiOF). Here, we suggest that can be taken the GW bandgap calculations of BiOCl as a reference to the place of experimental values. Under an external electric field, we succeed to reduce easily and quickly the bandgaps energy of our compounds. Besides, we show that under an external electric field a semiconductor can be changed to a metal with a strong field of more than 0.5 V/Å. In this framework, we have shown that this strategy is better than the incorporation method for engineering in order to find material with a bandgap that we want. We found that the dramatic redshift of the peaks at the BSE level as compared to DFT and RPA indicates strong excitonic effects.