[Wien] issues related to mBJ

[Peter Blaha]

> 1) I have nicely done the GGA SCF calculations for my compounds. The calculation has printed the three files cited above.
>
> 2) now, for wien2k_11.1, the steps to do an mBJ calculatiion were:
>
> a) cp $WIENROOT/SRC templates/case.inm vresp case.inm vresp
> b) run one more scf-cycle (use run lapw -NI -i 1) to generate the required case.vresp*
> files.
> c) “save” the LDA (PBE) calculation
> d) edit case.in0 and change the functional to option indxc=28.
> e) cp case.in0 case.in0 grr and change indxc in case.in0 grr to 50
> f) edit case.inm and change to PRATT mixing.
> g) run another scf cycle.
>
> First: my step b) is lasting for a bit too much time. I mean, it is only one scf cycle...but, I do not know why, it is lasting really too long. Maybe it is necessary to
> change the value of the mixing parameter in .vresp to a lower value (0.2 for example) already at step a), when one copies such file from SRC_template ?

This is just one iteration of an scf cycle, which is necessary to provide case.vresp needed
for the mBJ potential. It should take (nearly) exactly the same time as a single scf-cycle
of a GGA calculation.
>
> Second: I guess step g) is NOT simply another single SCF cycle (-i 1), but more than one. Am I wrong ?

Yes, this should of course be a full scf-calculation (usually with MANY cycles, since in particular
in your old wien2k-version it may have difficulties with convergence.

> Third: when one is arrived at completing step g, I guess that the files .vcoul, .r2v and clmsum are printed again, now in the mBJ picture. Right ?

Since mBJ requires R2V in case.in0, you get at the end the scf-mBJ vcoul, r2v and clmsum files.

> Fourth: if the question to the third answer is yes, then I would like to know if such files (especially vcoul and r2v) contain ALL the necessary information related to the
> potential.

Yes, vcould and r2v contains ALL the information. At the beginning the radial coefficients of the
angular momentum expansion are printed, at the end the fourier coefficients of the potentials.

> I try to explain myself better. I would like to recycle a real space code (let's call it code B) which can indeed read some files from wien2k (code A), and that can do
> calculations either with multiple scattering in the muffin tin approximation or with full potential mode (this option is based on the finite difference method). I have
> already interfaced this full potential MS code to another code that calculates resonant excitations (code C). However, now, I am asking myself if I can really give the
> vcoul, r2v and clmsum file to such codes (B and C)  when calculation from A is  mBJ or any other hybrids. I cannot ask to the one who developed long time ago the code B,
> and in any case it seem only LDA was used at that time to be plugged in into such code.  Now, I guess that the files .vcoul and .r2v (and clmsum) are related to the region
> INSIDE the spheres, so if I plug these files into my codes (B and C) I somehow I loose the non-local contribution outside the spheres, if my calculation with wien2k was
> done with mBJ or an hybrid functional.  Am I saying something completely wrong ? Am I missing something ?

As mentioned above, these files contain the potential for the spheres (both, the spherical (muffin-tin) and
non-spherical contributions. But these files contain also the info about the interstitial.

If your codes A,B or C are multiple scattering codes which have ONLY "spheres" (overlapping ones ?),
you need to expand the interstitial potential into spherical harmonics ("increasing our atomic spheres
to yours"). This was discussed  some time ago (1-2 years) in several emails on the mailing list.

PS: Everything said above holds for "local" potentials (like mBJ). A "hybrid" DFT cannot be represented
that way and these potentials files contain only then only the local part, but not the non-local HF.

-- 
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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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