[Wien] modified BJ potential calc.

[Peter Blaha]

Clearly, mBJ is only a POTENTIAL, not an energy-functional.
In fact, the mBJ option in WIEN2k uses the PBE-energy-functional, but
of course with the electron density (and spin-density) corresponding
to mBJ.

The question whether you can trust the mBJ/PBE results more than the PBE/PBE
results is not so easy to answer and may depend on the specific case.

If your compound belongs somehow to the cuprate-family (with CuO2 planes
and a Cu2+ ios) and you should get a significant Cu-moment. the chances are high
that PBE does not get the correct groundstate (insulator ? magnetism ?), i.e.
both the PBE-density and the PBE-energy are "wrong".

The mBJ-density should be more reliable in this case and maybe ??? the
PBE-energy for such a density is "better".

At least I would "backup" the mBJ results by some LDA+U or hybrid-DFT
calculations.

Am 06.04.2011 05:38, schrieb davgumo:
> Dear Wien users and Dr. Blaha
>
> I have been performing first-principles calculations on a recently synthesized crystal structure CuZrTiO5.
> This is a copper oxide the exhibits some potential to be a high Tc superconductor under doping.
>
> First I was interested in finding the ground state, which according to PBE calculations turns out to be in some antiferromagnetic order. After this I was interested in
> using mBJ to calculate an accurate value for the band gap, so I performed mBJ calculation on this antiferromagnetic order where I found the lowest energy. Recently I
> decided to run mBJ calculations on all the possible magnetic cases for this crystal. To my big surprise when I checked the energies calculated with mBJ the lowest energy is
> not longer on the magnetic configuration I found the ground state to be according to the PBE calculation.
>
> My question is if mBJ calculations are meant only to improve the band gap and will not provide the ground state of the system
>
> I appreciate any comments, hints, critics, etc that can help me to figure this out, and get a better understanding of the mBJ potential.
>
> Thank you very much.
>
> I can provide more details if this is not clear.
>
> David Guzman M
>
> Department of Physics&  Astronomy
> California State University-Los Angeles
>
>
>
>
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-- 
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Peter Blaha
Inst. Materials Chemistry, TU Vienna
Getreidemarkt 9, A-1060 Vienna, Austria
Tel: +43-1-5880115671
Fax: +43-1-5880115698
email: pblaha at theochem.tuwien.ac.at
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