Loop.s

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This is an example loop for finding the lattice constant of an FCC primitive cell (a rhomboeder: see the figure below for elements appearing in FCC lattice).

Crystal Structures of The Elements (for usual form at room temeperature).

The loop creates a series of POSCAR files with primitive cell size length specified in the seq command (3.1 to 4.0 Å with steps of 0.1 Å, i.e. 10 runs).

This cell size parameter, cell volume from OUTCAR and energy form OSZICAR are extracted into the output files.

Evaluation using a proper EOS method (preferentially the Murnaghan equation or Birch-Murnaghan equation) should follow.

Important Do not use quadratic regression (second order polynom)! - it's not an equation of state (EOS)!! Some tools for the non-linear fitting of Murnaghan Equation are listed online here: Online Resources for Calculating the Equation of State)

Note In the INCAR file, please take care that you set up a rigid calculation - NSW=1 - and that the electronic density is properly converged - NELMIN=10. The KPOINTS should define a very dense k-point grid (such as 10x10x10 or more).

The script loop.s itself:

#!/bin/bash
#$ -N Cu-lattice
#$ -pe c8m24_ompi 8
#$ -cwd
#$ -o vasp-ompi.out
#$ -e vasp-ompi.err
#$ -S /bin/bash
 
. /etc/profile.d/modules.sh

module load vasp/5.2
export OMP_NUM_THREADS=1

for L in `seq -f %3.1f 3.2 0.1 4.0`
do
cat >POSCAR <<!
Copper bulk - Cu1
  $L
    0.500000000000000   0.500000000000000   0.000000000000000
    0.000000000000000   0.500000000000000   0.500000000000000
    0.500000000000000   0.000000000000000   0.500000000000000
  1 
Selective dynamics
Direct
    0.000000000000000   0.000000000000000   0.000000000000000   T   T   T
!

echo "a= $L"
mpirun -np $NSLOTS vasp

V=`grep "volume " OUTCAR | tail -1 | awk '{print $5}'`
E=`tail -1 OSZICAR | awk '{print $5}'`

printf "%3.1f %6.2f %13.7f\n" $L $V $E >> SUMMARY-LVE.log
printf "%3.1f %13.7f\n" $L $E >> SUMMARY-LE.log
printf "%6.2f %13.7f\n" $V $E >> SUMMARY-VE.log
cp OSZICAR OSZICAR-$L
cp  OUTCAR  OUTCAR-$L
done

rm -f CHG* WAVE*

--Dkarhanek 13:53, 15 December 2010 (CET)