Fcc Si: Difference between revisions

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*Fcc Si lattice constant of 3.9 <math>\AA</math>.
*1 atom per unit cell.


=== {{TAG|INCAR}} ===
=== {{TAG|INCAR}} ===
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   11 11 11
   11 11 11
   0  0  0
   0  0  0
*Equally spaced k mesh.
*Odd number of k points in each direction results in a <math>\Gamma</math> centered mesh.
*56 k points in IBZ.


== Calculation ==
== Calculation ==
*Calculate energy for different lattice parameters.
*Fit to some equation of states to obtain the equilibrium volume.


*The bash-script <tt>loop.sh</tt> runs fcc Si at several different lattice constants (3.5-4.3 Å) and collects free energy versus lattice constant into the file SUMMARY.fcc
*The bash-script <tt>loop.sh</tt> runs fcc Si at several different lattice constants (3.5-4.3 Å) and collects free energy versus lattice constant into the file SUMMARY.fcc

Revision as of 14:07, 4 May 2017

Task

Lattice constant optimization for 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
  • Fcc Si lattice constant of 3.9 .
  • 1 atom per unit cell.

INCAR

System = fcc Si
ISTART = 0 ; ICHARG = 2
ENCUT = 240
ISMEAR = 0; SIGMA = 0.1
  • Initial charge density form overlapping atoms.
  • Energy cutoff of 240 eV from POTCAR file.

KPOINTS

k-points
 0
Monkhorst Pack
 11 11 11
 0  0  0
  • Equally spaced k mesh.
  • Odd number of k points in each direction results in a centered mesh.
  • 56 k points in IBZ.

Calculation

  • Calculate energy for different lattice parameters.
  • Fit to some equation of states to obtain the equilibrium volume.
  • The bash-script loop.sh runs fcc Si at several different lattice constants (3.5-4.3 Å) and collects free energy versus lattice constant into the file SUMMARY.fcc
#! /bin/bash
BIN=/path/to/your/vasp/executable
rm WAVECAR SUMMARY.fcc
for i in  3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 4.3 ; do
cat >POSCAR <<!
fcc:
   $i
 0.5 0.5 0.0
 0.0 0.5 0.5
 0.5 0.0 0.5
   1
cartesian
0 0 0
!
echo "a= $i" ; mpirun -np 2 $BIN
E=`awk '/F=/ {print $0}' OSZICAR` ; echo $i $E  >>SUMMARY.fcc
done
cat SUMMARY.fcc

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).

  • To make a quick plot of SUMMARY.fcc try:
gnuplot
gnuplot> plot "SUMMARY.fcc" using ($1):($4) w lp

Download

fccSi.tgz


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