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
Tel.: +43-(0)316-380-8564

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