[Pw_forum] Si band gap calculated with different functionals

[Danilo Neuber]

On Sat, 29 Nov 2003, Paolo Giannozzi wrote:

> is the lattice parameter
> - the same for all cases, and equal to the experimental one
> - the theoretical one for each case, and they are very similar
> - the theoretical one for each case, but they are not very similar
> - none of the above ?

Dear Mr. Giannozzi!

The lattice constant was a_0 = 10.2 Bohr in all my previous calculations
(according to Ashcroft & Mermin: "Solid State Physics" the experimental
value is a_0 = 5.43 Angstrom = 10.26 Bohr).

I did some more calculations with my PPs varying the lattice constant a_0
from 10.1 to 10.5 Bohr this time:

  PP: Si_blyp.mt (by DRN)
  -----------------------
  E_cut[Ry]    a_lat[Bohr]     E_tot [Ry]    E_gap [eV]
  70.0         10.20           -15.57266012  0.855
               10.30           -15.57527183  0.897
>>	       10.40           -15.57643309  0.935<<
	       10.50           -15.57627761  0.971

  PP: Si_lda.mt (by DRN)
  ----------------------
  E_cut[Ry]    a_lat[Bohr]     E_tot [Ry]    E_gap [eV]
  30.0         10.10           -15.85440094  0.463
  30.0         10.15           -15.85487606  0.488
>>30.0         10.20           -15.85500476  0.510<<
  30.0         10.25           -15.85475781  0.533
  30.0         10.30           -15.85413174  0.555

  PP: Si_pbe.mt (by DRN)
  ----------------------
  E_cut[Ry]    a_lat[Bohr]     E_tot [Ry]    E_gap [eV]
  30.0         10.10           -15.72409215  0.537
  30.0         10.20           -15.72726160  0.589
  30.0         10.30           -15.72883722  0.638
>>30.0         10.40           -15.72895958  0.684<<
  30.0         10.50           -15.72773301  0.727


I modified the shell script of example 5 (pw_examples) a bit but I did
not change the k-point meshes, so E_gap is not accurate to three digits -
is it necessary to use a denser k-point mesh for my tests?

Do you think these results are reasonable (at least for the LDA and
PBE pseudopotentials)? Which further tests would you suggest?

Thank you very much for your help and your comments!

With kind regards,

Danilo Neuber

-- 
Dipl.-Ing. Danilo Neuber <neuber at itp.tu-graz.ac.at>

Technische Universität Graz               Telefon: +43 / 316 / 873 - 8188
Institut für Theoretische Physik          Telefax: +43 / 316 / 873 - 8678
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