SCF Calculation for Silicon

Once the Installation for Quantum Espresso is done, we can go ahead and perform some basic calculations. Here we will do that for Silicon.

Self consistent field calculation for silicon¶

Input Files¶

Inorder to perform the SCF we need information about Silicon which is provided in pw.scf.silicon.in (pw.scf.silicon.in) whose content is as following :

Tip

The naming convention is like this ;

pw : plane waves,

scf : the file is to be used for scf calculation only,

silicon : name of the material

in : input file

&CONTROL
  calculation = 'scf',

  prefix = 'silicon',

  outdir = './'

  pseudo_dir = './'

  verbosity = 'high'
/

&SYSTEM
  ibrav =  2,

  celldm(1) = 10.26,

  nat =  2,

  ntyp = 1,

  ecutwfc = 30

  nbnd = 8
/

&ELECTRONS
  mixing_beta = 0.6
/

ATOMIC_SPECIES
  Si 28.086 Si.pbe-n-kjpaw_psl.1.0.0.UPF

ATOMIC_POSITIONS (alat)
  Si 0.0 0.0 0.0
  Si 0.25 0.25 0.25

K_POINTS (automatic)
  6 6 6 0 0 0

We also need pseudopotential for Silicon, which can be downloaded from here and kept in the working directory. Make sure that the name of the pesudopotential matches with the name in input file. (We have used Si.pbe-n-kjpaw_psl.1.0.0.UPF in this exampl)

ATOMIC_SPECIES
  Si 28.086 Si.pbe-n-kjpaw_psl.1.0.0.UPF

Now we can go ahead and start the SCF calculation by simply typing this in Terminal

pw.x < pw.scf.silicon.in > pw.scf.silicon.out

Or for parallel calculation, we can do

mpirun -np 4 pw.x -inp pw.scf.silicon.in > pw.scf.silicon.out

Note

The executables should already be in the PATH but if the above command throws error, then we can add full path to the executable to run the code. mpirun -np 4 /usr/bin/pw.x < pw.scf.silicon.in > pw.scf.silicon.out

Now let’s look at the output file pw.scf.silicon.out and see how the convergence is reached:

grep -e 'total energy' -e estimate pw.scf.silicon.out

Once SCF is converged, we can do Band structure calculation for Silicon.