Hello. I am currently doing computational DFT on a CsGeBr3 (3x3) perovskite monolayer to study its band structure and band gap for my undergraduate thesis, especially with Fe-doping and Biaxial Strain-inducement. I am using Quantum Espresso with BURAI as the GUI and here are the computed results in its band structure:
For the Pristine monolayer, the band gap is at 1.70 eV, which sounds reasonable enough for most expected semiconductors. However, when the computed results for the band structure and band gap for the Fe-doped monolayer came in (Fe-doped at 11.1%), the band gap significantly dropped all the way down to 0.22 eV. Both my adviser and one of my panelists have remarked such finding as rather unrealistic, and unfortunately it is beyond my current knowledge and understanding to ascertain whether such doping level can leave such significant changes to the band gap of my perovskite material, aside from making new computations with new parameters. I am currently seeking advice and help from other material scientists out there with this problem.
Uriel Mendez this results is reasonable.Different doping materials can be used to change the electronic and optical properties of ABX3 type materials. The maximum point of the valence band, and the minimum point of the conduction band may change. Depending on the degree of doping, there may be significant changes in the band shape of the material. There are various reports on the electronic band behavior of the material after doping; for example, there are materials that can have a direct → indirect or indirect → direct band gap other than metallic behavior.
Another consideration is that if your supercell cell is a cube of 10 A (I don’t know the actual structure of your compound), then adding one electron in such structure corresponds to roughly a doping of 10^21 e/cm^3. This is equivalent to very high doping, that is indeed saturating your bands. You should try to enlarge your supercell. I know this is not cheap, but doping in a material is indeed a difficult calculation.
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