[Wien] Controversy in band gap values CoSb

[Peter Blaha]

You missed an important comment:

CoSb3.scf::GAP  :    0.0502 Ry =     0.683 eV   (provided you have a 
proper k-mesh)

PROVIDED YOU HAVE A PROPER K-MESH.
We discussed this several time in the mailing list. If you do the 
scf-cycle with a shifted k-mesh and the gap is at gamma, the reported 
gap in the scf-file (or the DOS) is NOT ok. (How should it know that the 
gap at gamma is smaller, when gamma is not calculated ??)

You can get a "correct" gap using an unshifted (but denser) k-mesh, or 
you read the gap value from the band structure.


Am 12.07.2013 08:54, schrieb wien-bounces at zeus.theochem.tuwien.ac.at:
Dear Prof, Blaha and Wien2k users,,

I'm looking for your urgent help about the following:

- I'm calculating DOS and band structure of CoSb3. I noted strange 
behaviour when comparing the values obtained from DOS and band 
structure. The analysis utility gives me a value of Eg equals to 0.684eV 
while the band structure shows crossing of Fermi level at G-point (i.e 
metallic). If I shifted manually the value of Eg in case.insp to match 
the top of the valence band the band gap appears to be ~ 0.4 eV. These 
values were obtained when I used mBJ scheme. I got similar behaviour 
when using GGA, but of course the Eg values are smaller.

- I have  doubt about something going wrong after preparing the required 
files for the band plot (may be in case.output1). This is because when I 
directly plot bands, i.e without - x lapw1 -band -up/-dn steps, I get 
the correct band gap. Of course the lines look not connected with no 
symmetry points written. However, I'm not sure about what input files I 
should provide to you, I attach case.struct, DOS and the cases of the 
band plots.


Analysis of parameter:
:FER :GAP
in CoSb3.scf (showing last 10 / 1 lines)

--- FER -----------
in  1 files:
CoSb3.scf::FER  : F E R M I - ENERGY(TETRAH.M.)=   0.5239017718
--- GAP -----------
in  1 files:
CoSb3.scf::GAP  :    0.0502 Ry =     0.683 eV   (provided you have a 
proper k-mesh)


I attach two files for plots of DOS and band structures


-- 
Osama
Prof Dr Osama Ali Yassin
Professor of Solid State Physics and ICTP regular associate
Department of Physics, Faculty of Science
Taibah University, A-Madinah Al-Munawarh, K. Saudi Arabia


-- 
Peter Blaha
Inst.Materials Chemistry
TU Vienna
Getreidemarkt 9
A-1060 Vienna
Austria
+43-1-5880115671
-- 
Peter Blaha
Inst.Materials Chemistry
TU Vienna
Getreidemarkt 9
A-1060 Vienna
Austria
+43-1-5880115671