[Wien] modified BJ potential calc.

[tran at theochem.tuwien.ac.at]

Hello,

Actually, this is the LDA (and not PBE) exchange-correlation functional
which is used for the energy when MBJLDA is used for the potential
(option 28).

If you want PBE for the energy you have to replace

      exu=2.d0*(exupls + eclsd)
      exd=2.d0*(exdnls + eclsd)
by
      exu=2.d0*(exuppb + ecpbe)
      exd=2.d0*(exdnpb + ecpbe)

in the part of the subroutine vxclm2.f which concerns option 28.
Then you recompile the lapw0 package.
Maybe, the antiferromagnetic state will be the lowest again?

F. Tran

On Wed, 6 Apr 2011, davgumo wrote:

> 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
> > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> 
> -- 
> -----------------------------------------
> 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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