[Wien] two mBJ questions

[Pavel Ondračka]

tran at theochem.tuwien.ac.at píše v Út 24. 11. 2015 v 14:32 +0100:
> Hi,
> 
> It seems that the LDA energy with the mBJ orbitals leads
> to the correct stability ordering. This sounds interesting, but
> is it for the right reason? In other words, is it because the shape
> of
> the mBJ orbitals is more correct than with LDA/PBE/hybrid?
> It's probably difficult to answer to this question. Beside this, in
> my
> opinion, there is nothing wrong (technically or theoretically) in
> using
> the LDA energies calculated with mBJ orbitals.

Thanks for the clarification.

> It's possible to use the PBE energy instead of LDA for the energy.
> If you are using a recent version of WIEN2k which uses keywords
> in case.in0 to specify the functional, then you need to specify
> this for PBE energy with mBJLDA for the potential:
> EX_PBE EC_PBE VX_MBJ VC_LDA
> 
Thanks a lot, my Wien2k version is the latest one.
> 
> The mBJ parameters were calibrated such that the mBJLDA potential
> reproduces at best the experimental band gaps. The energy was not
> used at all in this procedure.
> 
> If my explanations are too complicated, then I will try to make
> more clear.
> 
> F. Tran
> 
Your explanation is perfectly clear. I think I understand now what
caused my confusion. IMHO there is a mistake in userguide on page 126,
Table 7.3: XC shortcut-switches. It shows that alternative to XC_MBJ is
EX_LDA EC_LDA VX_MBJ VC_MBJ.

So when I tried to use PBE energy for the first time, I took the long
notation for XC_MBJ from userguide and replaced LDA with PBE, except than I got an
error: 'VXCLM2 - Correlation-potential calculation not supported for'
- MBJ
So I removed VC_MBJ, however I forgot to replace it with VC_LDA, I got
some bogus results and that started my confussion.

Thanks for clearing this up.
Best regards
Pavel Ondračka