[Pw_forum] can one do hybrid calculations with smearing

[Ari P Seitsonen]

Dear Rajdeep Banerjee,

   Some smearing schemes lead to negative occupation numbers. If you are 
using this only for the DOS in a semi-conductor, you could as well use the 
Fermi-Dirac broadening scheme (or Gaussian).

   To understand why, well please refer to the mathematical form of the 
functions in the original literature and apply them (analytically) to 
semi-conductors. :)

     Greetings,

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
   Institut für Chemie der Universität Zürich, CH-8057 Zürich
   Tel: +41 44 63 54 497  /  Mobile: +41 79 71 90 935

On Thu, 8 May 2014, Rajdeep Banerjee wrote:

> Dear all,
>            I was calculating band gap with hybrid functionals for a
> semiconductor. If I don't use smearing (i.e. occupations = 'fixed') the dos 
> seems ok but whenever I use smearing and plot dos, at some energies I get
> negative density of states ! I can't understand why this is happening.
> Can/should one use smearing for hybrid functionals? Following is the
> important part of the input:
> 
>  &system
>     ibrav = 4,
>     celldm(1) = 6.474424, celldm(3) = 5.837554613 ,
>     nat = 10, ntyp = 3,
>     ecutwfc = 40,
>     london = .true.,
>     nbnd = 25,
>     occupations = 'smearing', smearing = 'mv', degauss = 0.001,
>     input_dft = 'hse',
>     exxdiv_treatment = 'gygi-baldereschi',
>     x_gamma_extrapolation = .true.,
>     nqx1 = 4, nqx2 = 4, nqx3 = 1
> 
> ...
> 
>     Another problem is that whenever I use smearing the output doesn't give
> HOMO-LUMO as it considers it as metal and prints only the fermi energy. So
> if I'm studying semiconductor to metal transition there's no way one can
> check the band gap change.
>                 
>     I'd be greatful if anyone can shine some light on above problems.
> 
> Thnaks,
> Rajdeep Banerjee
> Ph. D. student
> JNCASR
> Bangalore, India
> 
>