[Wien] modified BJ potential calc.

[davgumo]

Dr. Blaha, thank you very much for your comments.

What is a bit confusing about my case is that my very first calculation with PBE identifies the ground state in some peculiar antiferromagnetic insulator (very small band gap though) this result was expected. Now when I try to improve the band gap by performing mBJ calcs, I find that this magnetic order which once I identified as the ground state is no longer lowest in energy. In fact, I found out that the nonmagnetic case is much lower in energy according to mBJ.

Once again, it was expected that the ground state would be found as an antiferromagnetic insulator as shown with PBE.

Do think that mBJ somehow has trouble determining the ground state for this crystal?

I appreciate so much your help and the time you devote to all the users.
 
By the way, we will soon have some experimental measurements about the band gap of this crystal, I hope the calculated mBJ band gap agrees with the experiment this would be very nice. 

David Guzman M
Department of Physics & Astronomy
California State University-Los Angeles
(310)528-4841

On Apr 05, 2011, at 10:42 PM, Peter Blaha <pblaha at theochem.tuwien.ac.at> wrote:

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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> Wien at zeus.theochem.tuwien.ac.at
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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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