[Wien] question about tetra's choice of Emax

[Peter Blaha]

The DOS is calculated up to a value for which we can guarantee that the 
DOS is correct and complete.

Of course, the DOS up to the highest band-maximum would be non-zero, but 
there is a chance that some (maybe a lot) of DOS is missing and a user 
would not notice this and "misintewrprete" this wrong DOS.

Now he can trust that the calculated DOS is ok, and if he needs higher 
DOS, he has to increase the emax in case.in1 and/or in case.int.

PS: You are probably using an older WIEN2k version, because now we use a 
"dynamical" Emax in case.in1, which takes the actual EF into account. 
But of course in cases of very steep bands above EF, the default in1 
file may still be insufficient.

PPS: In your situation it could even be, that the scf calculation is 
"wrong", since you occupied the wrong bands ....

Am 15.11.2016 um 19:12 schrieb pieper:
> Hello, mailing list,
>
> yesterday I had for the first time some dispute with the way tetra
> automatically chooses its input energy range. I would like to understand
> why the particular automatic choice of Emax was introduced.
>
> Until then it worked so well that I didn't even notice that Emax is
> automatically adjusted, but then I wanted to illustrate Wien2k by
> calculating the example fcc Ni. I took Co instead of Ni, lattice
> constant adjusted to 6.637, RMT to touching spheres. I used w2web for
> initialiazation and initiating scf, kgen with 10000 vectors,
> spin-polarized in an FM starting configuration, no spin-orbit coupling.
>
> Then I chose DOS from the Tasks menu, skipped the optional steps lapw1
> and qtl, used lapw2 -qtl, configured .int to calculate just the total
> DOS (the default). When I proudly presented the result of dosplot to a
> visitor the plot ended below the Fermi energy ...
>
> Increasing Emax in .int did nothing, as the experts probably could have
> told me beforehand. The (in this case in my view annoying) automatic
> choice of Emax that kicks in is indicated in the header of .outputtup
> (as well as in the user guide - and yes, I know one should read it):
>
> .
> .
> .
> BAND LIMITS OF BAND   8 ARE   0.40511   0.51502
> BAND LIMITS OF BAND   9 ARE   0.43442   1.04422
>   EMAX reduced due to lower HIGHEST BAND-minimum
>  EMIN, DE, EMAX              :  -0.50000   0.00200   0.43442
>
> The problem in this case is that the 'lower highest Band-minimum' is
> BELOW the Fermi-energy:
>
>  ******** EF and DOS at fermi level *******
>   0.56702     0.00              0.00
>
> So one MUST go back to the (in principle optional) lapw1 step with some
> larger Emax in .in1 (as indicated in the DOS menu and in the UG).
> Increasing Emax there appears to me a little clumsy since one has to
> guess an Emax that will generate a band with a band minimum above E_F.
>
> Why not have tetra choose Emax as the minimum of the Emax input in .int
> and the highest Band-MAXIMUM?
>
>
> ---
> Dr. Martin Pieper
> Karl-Franzens University
> Institute of Physics
> Universitätsplatz 5
> A-8010 Graz
> Austria
> Tel.: +43-(0)316-380-8564
>
>
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-- 
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
WWW:   http://www.imc.tuwien.ac.at/staff/tc_group_e.php
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