下面以Si晶体为例，计算态密度。

STEP 1

Input file:

&control
    calculation = 'scf'
    restart_mode = 'from_scratch'
    prefix = 'si'
    outdir = './outdir'
    pseudo_dir = '/BIGDATA1/ac_iphy_jrsun_1/soft/QE/SSSP'
/
&system
    ibrav=2, celldm(1) =10.4109, 
    nat=2, ntyp=1,
    ecutwfc=50
/
&electrons
    conv_thr=1e-8
/
ATOMIC_SPECIES
 Si  28.0855  Si.pbe-n-rrkjus_psl.1.0.0.UPF

ATOMIC_POSITIONS (alat)
 Si 0.00 0.00 0.00 
 Si 0.25 0.25 0.25 
K_POINTS (automatic)
  8 8 8 0 0 0

We increase the energy cutoff and the k-grid density to get the self-consistent charge density.

STEP 2

Input file:

&control
    calculation = 'nscf'
    restart_mode = 'from_scratch'
    prefix = 'si'
    outdir = './outdir'
    pseudo_dir = '/BIGDATA1/ac_iphy_jrsun_1/soft/QE/SSSP'
/
&system
    ibrav=2, celldm(1) =10.4109, 
    nat=2, ntyp=1,
    ecutwfc=50
    occupations='tetrahedra'
/
&electrons
    conv_thr=1e-8
/
ATOMIC_SPECIES
 Si  28.0855  Si.pbe-n-rrkjus_psl.1.0.0.UPF

ATOMIC_POSITIONS (alat)
 Si 0.00 0.00 0.00 
 Si 0.25 0.25 0.25 
K_POINTS (automatic)
  12 12 12 0 0 0

New tags:
‘occupations’:

'smearing' :
gaussian smearing for metals;
see variables smearing and degauss
            
'tetrahedra' :
Tetrahedron method, Bloechl's version:
P.E. Bloechl, PRB 49, 16223 (1994)
Requires uniform grid of k-points, to be
automatically generated (see card K_POINTS).
Well suited for calculation of DOS,
less so (because not variational) for
force/optimization/dynamics calculations.
            
'tetrahedra_lin' :
Original linear tetrahedron method.
To be used only as a reference;
the optimized tetrahedron method is more efficient.
            
'tetrahedra_opt' :
Optimized tetrahedron method:
see M. Kawamura, PRB 89, 094515 (2014).
Can be used for phonon calculations as well.
            
'fixed' :
for insulators with a gap
            
'from_input' :
The occupation are read from input file,
card OCCUPATIONS. Option valid only for a
single k-point, requires nbnd to be set
in input. Occupations should be consistent
with the value of tot_charge.

We increased the energy cutoff for wavefunctions and the k-mesh. Here we can obtain the E-fermi in *.out by $grep Fermi si.2_nscf.out$:
the Fermi energy is 6.1331 ev

STEP 3

We do the dos calculation using dos.x. Before two steps are using pw.x.

Input file:

&DOS
    prefix='si'
    outdir='./outdir/'
    fildos='si.dos.dat'
    emin=-9.0
    emax=16.0
/

Tags:
‘prefix’: prefix of input file produced by pw.x
‘outdir’: directory containing the input data, i.e. the same as in pw.x
‘fildos’: output file containing DOS(E)
‘emin,emax’: min, max energy (eV) for DOS plot
‘DeltaE’: energy grid step (eV)

After yhbatch -N 1 -n 24 -p bigdata ./qe.sh dos.x, we obtain the si.dos.dat file, and we plot this:

And we find the energy gap is around 0.75 eV (underestimated by DFT compared with experimental 1.17 eV)