Cd Si

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Task

Volume relaxtion of cubic diamond (cd) Si and the calculation of the DOS and bandstructure.

Input

POSCAR

cubic diamond
   5.5
 0.0    0.5     0.5
 0.5    0.0     0.5
 0.5    0.5     0.0
  2
Direct
 -0.125 -0.125 -0.125
  0.125  0.125  0.125

Diamond Si starting lattice constant of 5.5 $\AA$ .
Fcc cell.
2 atoms in cell.

INCAR

System = diamond Si
ISTART = 0 ; ICHARG=2
ENCUT  =    240
ISMEAR = 0; SIGMA = 0.1

KPOINTS

k-points
 0
Monkhorst Pack
 11 11 11
 0  0  0

Calculation

The calculation of the optimized volume. DOS and bandstructure is similar as in the examples fcc_Si, fcc_Si_DOS and fcc_Si_bandstructure, respectively.

Volume relaxation

The bash-script loop.sh runs Si in the cubic diamond (cd) structure at several different lattice constants (5.1-5.7 Å) and collects free energy versus lattice constant into the file SUMMARY.dia:

#! /bin/bash
BIN=/path/to/your/vasp/executable
rm WAVECAR SUMMARY.dia
for i in  5.1 5.2 5.3 5.4 5.5 5.6 5.7 ; do
cat >POSCAR <<!
cubic diamond
   $i 
 0.0    0.5     0.5
 0.5    0.0     0.5
 0.5    0.5     0.0
  2
Direct
 -0.125 -0.125 -0.125
  0.125  0.125  0.125
!
echo "a= $i" ; mpirun -n 2 $BIN
E=`awk '/F=/ {print $0}' OSZICAR` ; echo $i $E  >>SUMMARY.dia
done
cat SUMMARY.dia

Example output of SUMMARY.dia:

5.2 1 F= -.10528151E+02 E0= -.10528137E+02 d E =-.274709E-04
5.3 1 F= -.10713281E+02 E0= -.10713280E+02 d E =-.218410E-05
5.4 1 F= -.10806685E+02 E0= -.10806685E+02 d E =-.114401E-06
5.5 1 F= -.10823039E+02 E0= -.10823039E+02 d E =-.429842E-08
5.6 1 F= -.10775102E+02 E0= -.10775102E+02 d E =-.204668E-09
5.7 1 F= -.10673578E+02 E0= -.10673578E+02 d E =-.112715E-10
5.8 1 F= -.10528393E+02 E0= -.10528393E+02 d E =-.552513E-11

To make a quick plot of SUMMARY.dia try:

gnuplot
gnuplot> plot "SUMMARY.dia" using ($1):($4) w lp

Extracted lattice parameter should be at 5.465 $\AA$ .

DOS

Enter correct volume of 5.5 $\AA$ into the POSCAR file.

Change the INCAR to DOS calculation (or use INCAR.dos):

System = diamond Si
ISTART = 0 ; ICHARG=2
ENCUT  =    240
ISMEAR = -5
LORBIT = 11

Run the script dos.sh to calculate the DOS.

Bandstructure

Mind: You will have to set the correct path to your VASP executable (i.e., BIN), and invoke VASP with the correct command (e.g., in the above: mpirun -np 2).

Download

diamondSi.tgz

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