[Pw_forum] Graphene_fixed calculation

[Ari P Seitsonen]

Dear Toshiharu Higuchi,

   How did you determine the band gap? Do you have a k point exactly at the 
point K of the Brillouin zone? I would guess no, and like I mentioned 
recently, I do not think that shifting the Monkhorst-Pack k point grid 
away from the Gamma (or Gamma-bar in two dimensions) point is a good idea.

     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 Tue, 27 May 2014, Higuchi Toshiharu wrote:

> 
> Dear Quantum-ESRESSO users,
> 
> I would like to calculate the local density of state of graphene and graphene
> 
> related materials.
> 
> Using the following pw.in file, I calculated the scf under “occupation = fixed”,
> 
> and get the HOMO = -0.8642 eV, and LUMO = -0.6635 eV. This results indicate
> 
> that this graphene is an insulator having a band gap of 0.2007 eV.
> 
> However, this model is half-metal having a band gap of 0.0 eV, if I calculated by
> 
> this process: (1)SCF (smearing) -> nscf (tetrahedra) -> ProjWFC.
> 
> Why will it become the error when I set ‘occupation = fixed’?
> 
> I would really appreciate if you teach me.
> 
> ******************************************************************
> 
> &CONTROL
> 
>                        title = 'Graphene_1A2' ,
> 
>                  calculation = 'scf' ,
> 
>                 restart_mode = 'from_scratch' ,
> 
>                       outdir = '/home/user/tmp/' ,
> 
>                   pseudo_dir = '/home/user/espresso-5.0.1/espresso-5.0.1/pseudo/' ,
> 
>                       prefix = 'Graphene_1A2' ,
> 
>                    verbosity = 'high' ,
> 
> /
> 
> &SYSTEM
> 
>                        ibrav = 4,
> 
>                    celldm(1) = 4.6595,
> 
>                    celldm(3) = 4.0571,
> 
>                          nat = 2,
> 
>                         ntyp = 1,
> 
>                      ecutwfc = 40 ,
> 
>                      ecutrho = 200 ,
> 
>                         nbnd = 150,
> 
>                  occupations = 'fixed' ,
> 
>                      degauss = 0.02 ,
> 
>                     smearing = 'gaussian' ,
> 
>             exxdiv_treatment = 'gygi-baldereschi' ,
> 
> /
> 
> &ELECTRONS
> 
>             electron_maxstep = 100,
> 
>                     conv_thr = 1.D-8 ,
> 
> /
> 
> ATOMIC_SPECIES
> 
>     C   12.01100  C.pz-rrkjus.UPF
> 
> ATOMIC_POSITIONS angstrom
> 
>     C      0.000000000    0.000000000    0.000000000   
> 
>     C      1.232850116    0.706423116    0.000000000   
> 
> K_POINTS automatic
> 
>   40 40 1   1 1 1
> 
>  
> 
> **************************************************************************************
> 
> Toshiharu Higuchi
> 
> University of Tsukuba/ Japan
> 
> E-Mail: toshihigu at r7.dion.ne.jp
> 
> **************************************************************************************
> 
>  
> 
> 
>