[Pw_forum] problems with Ta2O5 compound

[Maxim Ivanov]

Hello all,
Has anyone work with Ta2O5 ? I have some problems with that compound. I am working with delta modification [1]. First of all energy gap is too small. It is about 1.5 eV, however for amorfous Ta2O5 experiments say it is about 4 eV. It is too big underestimation of Eg. Moreover I have not find defect level in 14, 42, 168 atoms supercells with oxygen vacancy in the center of the cell.I have made LDA+U calculations. I found that Hubbard U is about 2 eV for supercell with 42 atoms, however no changes happened. Eg has slightly increased but no defect level appeared.Ta has 3 d electrons and is described by ultrasoft pseudopotential. I took it from pwscf.org. It might be problem in the potential. What do you think about all of these?
[1] A. Fukumoto and K. Miwa,
Phys. Rev. B 55, 11 155 (1997)


      
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