### Author Topic: charged_defects  (Read 643 times)

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#### NW

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##### charged_defects
« on: July 26, 2022, 15:23 »
Hello,

I have a question regarding the following tutorial about charged defects formation energy.
https://docs.quantumatk.com/tutorials/charged_defects/charged_defects.html

It is mentioned that "E_VBM is the valence band maximum as given by the ATK band structure calculation for the bulk material of study". My question is how QATK takes VBE? because if we draw the bandstructure via the available tool for that in QATK, then automatically the Fermi energy is set at zero and all the bands are shifted accordingly. So the printed VBE is not the absolute VBE and it is VBE+E_fermi shifting. Am I right? if yes, how one can determine the correct value for VBE via QATK for charge defect calculations?

Thanks

#### Anders Blom

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##### Re: charged_defects
« Reply #1 on: July 27, 2022, 09:28 »
I would generally would strongly recommend to use the SMW components for charged point defect calculations (https://docs.quantumatk.com/tutorials/smw_defects/smw_defects.html).

But the manual approach actually has all script needed and there is even a function in one of them (formation-energies.py) called "get_vbm" which shows exactly what is done. In short, the distance of the VBM to the Fermi level is added to the absolute value of the Fermi energy to get E_VBM in "absolute" terms. Of course, there are no absolute energy so we really just a new reference point, this time the pseudopotential vacuum.

#### NW

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##### Re: charged_defects
« Reply #2 on: August 1, 2022, 10:16 »
Dear Anders,

Thanks

#### Anders Blom

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##### Re: charged_defects
« Reply #3 on: August 30, 2022, 21:46 »
Not as such, but you don't have to work only with structure in the database, it's just a convenient way to define the structure and suggest calculators. The functionality for the CPD etc works fine with just your own calculator and atomic structure. If that is not obvious, let me know and we can find some example