[Pw_forum] Germanium bulk band structure

[Giuseppe Mattioli]

Dear Priyank
Short answer: use an hybrid functional such as HSE. Bulk Ge is a metal with every flavour of GGA.
HTH
Giuseppe


On Thursday, February 04, 2016 12:12:32 PM Michael Schofield wrote:
> Dear sir/madam,
> 
> I am trying to calculate the bulk band structure for Germanium using GGA
> exchange-correlation with PAW basis, but the band gap is coming out to be
> almost zero. I know DFT underestimates the band gap but it is coming almost
> zero (~0.03eV). Is there any means by which I can get more accurate band
> gap.
> 
> My input script is here:
> 
> 
> &control
>  calculation = 'nscf',
>  verbosity = 'high',
>  restart_mode = 'from_scratch',
>  prefix = 'Ge_bulk_nscf',
>  tstress = .false.,
>  tprnfor = .false.,
>  pseudo_dir = '/home/Software/QE/pseudopotentials/upf_files/',
>  outdir = './output/'
> /
> 
> &system
>  ibrav=2,
>  celldm(1) = 10.690937,
>  nat=2, ntyp=1,
>  nbnd = 12,
>  ecutwfc=60,
>  ecutrho= 600,
> /
> 
> &electrons
>  diagonalization='david',
>  mixing_mode = 'plain',
>  mixing_beta = 0.7,
>  conv_thr =  1.0d-6,
>  electron_maxstep = 500,
> /
> 
> ATOMIC_SPECIES
>  Ge 72.640000 Ge.pbe-kjpaw.UPF
> 
> ATOMIC_POSITIONS crystal
>  Ge 0.000000 0.000000 0.000000
>  Ge 0.250000 0.250000 0.250000
> 
> K_POINTS crystal_b
> 6
> 0.0   0.0    0.0   100
> 0.0   0.5    0.0   100
> 0.0   0.375 -0.375 100
> -0.25 0.25  -0.5   100
> -0.5  0.0   -0.5   100
> 0.0   0.0    0.0   1
>  -----------------------------------------------------------------
> PFA the band structure I am getting from it.
> 
> Any help/suggestions will be helpful.
> 
> 
> 
> 
> Thanks
> Priyank
> Dept. of EE
> IIT Kanpur, India

********************************************************
- Article premier - Les hommes naissent et demeurent
libres et égaux en droits. Les distinctions sociales
ne peuvent être fondées que sur l'utilité commune
- Article 2 - Le but de toute association politique
est la conservation des droits naturels et 
imprescriptibles de l'homme. Ces droits sont la liberté,
la propriété, la sûreté et la résistance à l'oppression.
********************************************************

   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
   v. Salaria Km 29,300 - C.P. 10                
   I 00015 - Monterotondo Stazione (RM), Italy    
   Tel + 39 06 90672836 - Fax +39 06 90672316    
   E-mail: <giuseppe.mattioli at ism.cnr.it>
   http://www.ism.cnr.it/english/staff/mattiolig
   ResearcherID: F-6308-2012