fcc Si bandstructure

Based on the VASP wiki example in this link

Task: Calculation of the bandstructure for fcc Si along L-Gamma-X-U and K-Gamma symmetry points.

Note that bandstructure calculations should be done in two steps (compare with the procedure for DOS):
(1) a self consistent, static, converged calculation and
(2) a non-self consistent calculation, using the charge density (CHGCAR) from the first, with k-points selected from an interesting path in the Brillouin zone.

First, copy the example folder which contains some of the VASP input files and useful scripts

cp -r /software/sse/manual/vasp/training/ws2020/fcc_Si_band .
cd fcc_Si_band

and copy the latest POTCAR file for Si

cp /software/sse/manual/vasp/POTCARs/PBE/2015-09-21/Si/POTCAR .

Input files

POSCAR

fcc Si
 3.9
 0.5 0.5 0.0
 0.0 0.5 0.5
 0.5 0.0 0.5
Si
   1
cartesian
0 0 0

INCAR

System = fcc Si

ICHARG = 11  #read charge file
ENCUT = 240
ISMEAR = 0
SIGMA = 0.1
LORBIT = 11

ICHARGE=11, perform a static calculation reading CHGCAR
ISMEAR=0, for bandstructure calculation

KPOINTS

k-points for bandstructure L-Gamma-X-U K-Gamma
 10
line
reciprocal
  0.50000  0.50000  0.50000    1 !L
  0.00000  0.00000  0.00000    1 !Gamma

  0.00000  0.00000  0.00000    1 !Gamma
  0.00000  0.50000  0.50000    1 !X

  0.00000  0.50000  0.50000    1 !X
  0.25000  0.62500  0.62500    1 !U

  0.37500  0.7500   0.37500    1 !K
  0.00000  0.00000  0.00000    1 !Gamma

k-points along the line L - Gamma - X - U and K - Gamma
10 points per line
Keyword line to generate bandstructure
Reciprocal coordinates
All points with weight 1

Calculation

Here we’ll assume that the first self consistent, static, step is done in the previous fcc Si example. Now perform a non-self consistent calculation, to do that copy CHGCAR from the previous example, e.g.

cp ../fcc_Si/3.9/CHGCAR .

and submit the job to the queue

sbatch run.sh

when the job has finished, check slurm-JOBID.out

cat slurm*.out

Plot the bandstructure using p4vasp

p4v &

and select: Electronic > DOS+bands > Show > Bands. As in the case of DOS, it’s possible to save the data by selecting Graph > Export, to e.g. raw data or an XmGrace file (.agr). Compare with the figure shown in the VASP wiki example.

Extra tasks

Have a look at the paths in the Brillouin zone for fcc by using the Bilbao crystallographic server, select: Space-group symmetry > KVEC > enter “225” for space group > Brillouin zone