[Pw_forum] for bandgap information

[Giuseppe Mattioli]

On the top of Nicola's suggestions, I would add some simple practical hints: you can found the band gap more easily if you ask the code to calculate a 
bunch of unoccupied states (which is not the case of your nscf calculation). See the "nbnd" variable in the INPUT_PW.txt manual for details. Moreover, 
l would check the structure because of this warning in the pw.x output

     Message from routine read_cards :
     DEPRECATED: no units specified in ATOMIC_POSITIONS card
     Message from routine read_cards :
     ATOMIC_POSITIONS: units set to alat

and because of the fact that pw.x does not find any symmetry operation in your apparently ordered cell. Are you sure you're using the correct units?
HTH
Giuseppe

 

On Monday, September 22, 2014 01:40:19 PM Nicola Marzari wrote:
> On 22/09/2014 13:23, Neeraj Goel wrote:
> > i have attached my CuInS2 , non- self consistent file. what is the
> > velue of badgap in this case. and how will i get this.
> > 
> >                                         regards
> >                                       
> >                                       Neeraj Goel
> >                                  
> >                                  Indian School of Mines
> 
> The direct band gap is going to be equal or smaller than {minus the highest
> occupied state plus the lowest unoccupied state} calculated at each key
> point, while the indirect band gap is going to be equal or smaller
> than {minus the highest occupied state at any key point} plus {the lowest
> occupied state at any k-point}.
> 
> As your mesh fineness increases, these values will converge to the right
> result,
> and if you'll understand also if the gap is direct or not.
> 
> *BTW, great if anyone could volunteer to include these calculations in
> the SCF and
> NSCF code (since they are very easy to do), with the due caveats.*
> 
> Ideally, a plot of the band structure along high-symmetry directions
> will help -
> do it first with germanium or silicon, and remember that the band
> structure in
> DFT is in any case not particularly good, and not meant in any formal sense
> to reproduce the correct quasiparticle excitations (even if the DFT band
> structure
> can be quite ok, a part from a smaller gap than you should have, if you use
> LDA or GGA, and quite good gaps if you use much more expensive HSE
> functionals or the
> like).
> 
> 				nicola
> 
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> > Pw_forum mailing list
> > Pw_forum at pwscf.org
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   Giuseppe Mattioli                            
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