Band structure of Silicon crystal - Quantum Espresso tutorial

In this session, I have taken FCC-Silicon as an example. but you can try for your own crystal structure. To plot band structure we have to clear with 3 input files. they are followed as,

1. scf input file = To calculate groundstate properties, Fermi energy
2. bands input file = To generate bands energy values for preferred k-points 
3. pp input file = To generate plottable data in Gnuplot/ origin/ etc

As we know from the previous session how to generate an input file for scf calculation. Since I have shown my input file for my silicon structure as below,
=========================================================================
&control
 calculation='scf',
 title='si',
 prefix='si',
 pseudo_dir='.',
 outdir='./tmp/'
/
&system
 ibrav=2,
 celldm(1)=10.2625,
 nat=2,
 ntyp=1,
nbnd =8,
 ecutwfc=60.0,
 ecutrho=720.0,
/
&electrons
 conv_thr = 1d-8
/
ATOMIC_SPECIES
 Si 28.08525 Si.pbe-rrkj.UPF
ATOMIC_POSITIONS crystal
Si -0.125 -0.125 -0.125
Si  0.125  0.125  0.125
K_POINTS automatic
4 4 4 1 1 1
========================================================================

In my pseudopotential file the silicon atom has 4 valance electrons as per two silicon atoms this will be counted as 8. so I choose nbnd as 8.

Bands input file followed as

=========================================================================
&control
 title='si',
 prefix='si',
 pseudo_dir='.',
 outdir='./tmp/',
 calculation='bands',
/
&system
 ibrav=2,
 celldm(1)=10.2625,
 nat=2,
 ntyp=1,
 ecutwfc=60.0,
 ecutrho=720.0,
 nbnd=8,
/
&electrons
 conv_thr = 1d-8
/
ATOMIC_SPECIES
 Si 28.0855 Si.pbe-rrkj.UPF
ATOMIC_POSITIONS crystal
Si -0.125 -0.125 -0.125
Si  0.125  0.125  0.125
K_POINTS 
 36
   0.5 0.5 0.5  1
   0.4 0.4 0.4  2
   0.3 0.3 0.3  3
   0.2 0.2 0.2  4
   0.1 0.1 0.1  5
   0.0 0.0 0.0  6
   0.0 0.0 0.1  7
   0.0 0.0 0.2  8
   0.0 0.0 0.3  9
   0.0 0.0 0.4 10
   0.0 0.0 0.5 11
   0.0 0.0 0.6 12
   0.0 0.0 0.7 13
   0.0 0.0 0.8 14
   0.0 0.0 0.9 15
   0.0 0.0 1.0 16
   0.0 0.1 1.0 17
   0.0 0.2 1.0 18
   0.0 0.3 1.0 19
   0.0 0.4 1.0 20
   0.0 0.5 1.0 21
   0.0 0.6 1.0 22
   0.0 0.7 1.0 23
   0.0 0.8 1.0 24
   0.0 0.9 1.0 25
   0.0 1.0 1.0 26
   0.0 0.9 0.9 27
   0.0 0.8 0.8 28
   0.0 0.7 0.7 29
   0.0 0.6 0.6 30
   0.0 0.5 0.5 31
   0.0 0.4 0.4 32
   0.0 0.3 0.3 33
   0.0 0.2 0.2 34
   0.0 0.1 0.1 35
   0.0 0.0 0.0 36
=======================================================================

since it is a fcc structure the high symettry points as L, Γ, M, X  = 4 k_points. but Silicon has 8 bands which results 36 kpoints. These k points were generated fro the Quantum espresso tools by following link [Q-E.materials cloud kpoint generator]. You can choose kpoints as your wish. But I have used tpa/2 kpoints here.

pp input file as followed as,

===========================================================

&BANDS

 outdir='./tmp/',

 prefix = 'si',

 filband = 'si_bands.dat',

/

===========================================================

Run commands as followed as,

pw.exe  <  Si.scf.in > Si.scf.out  # for scf calculation

pw.exe < Si.bands.in > Si.bands.out  # for bands calculation

bands.exe <Si.bands.pp.in > si.bands.pp.out  # for plot files generation

 To download input files click here.
after running the pp file you may get the potable file as in .gnu format the can be plotted from Gnuplot and origin. plot format is followed here.

fermi level can be found from the scf output file. if you want to plot E_F as zero,  you have to subtract the y data by fermi energy. To calculate Fermi level you must to run nscf calculation.Download example nscf input

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