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# Fcc Si DOS

Calculation of the DOS in fcc Si.

## Input

### POSCAR

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

### INCAR

```System = fcc Si
# ICHARG = 11 #charge read file
ENCUT  =    240
ISMEAR = -5 #tetrahedron
LORBIT = 11
```

### KPOINTS

```k-points
0
Monkhorst Pack
21 21 21
0  0  0
```

## Calculation

• Perform a static (NSW=0, IBRION=-1) self consistent calculation for the DOS (the DOS is found in the DOSCAR file.
• For large systems:
• Converge with a small number of k points.
• Increase the number of k points for the DOS and set ICHARG=11 (charge density from the last self-consistent run). ICHARG=11 treats each k point independently and keeps the charge density and the potential fixed.
• Read CHGCAR from previous run. To copy the self-consistent charge density of example fcc_Si to your current working

directory (assumed to be fccSidos), type: \$ cp ../fccSi/CHGCAR . You must do this otherwise VASP can not read the CHGCAR and will terminate.

• The smearing of the k points is set to the tetrahedron method with Blöchl corrections (ISMEAR=-5 to fi the problem
• To plot the DOS use p4vasp:

• Alternatively the bash-script plotdos.sh invokes awk and gnuplot to get the DOS from the vasprun.xml file and plot it.
```awk 'BEGIN{i=1} /dos>/,\
/\/dos>/ \
{a[i]=\$2 ; b[i]=\$3 ; i=i+1} \
END{for (j=12;j<i-5;j++) print a[j],b[j]}' vasprun.xml > dos.dat

ef=`awk '/efermi/ {print \$3}' vasprun.xml`

cat >plotfile<<!
# set term postscript enhanced eps colour lw 2 "Helvetica" 20
# set output "optics.eps"
plot "dos.dat" using (\\$1-\$ef):(\\$2) w lp
!

gnuplot -persist plotfile

rm dos.dat plotfile
```