# Thirdorder ¼ÆËã

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#Running thirdorder with VASP #

1. Prepare input files for vasp calculations.

Any invocation of thirdorder_vasp.py requires a POSCAR file with a description of the unit cell to be present in the current directory. The script uses no other configuration files, and takes exactly five mandatory command-line arguments:

bash

thirdorder_vasp.py sow|reap na nb nc cutoff [nm/-integer]



sow|reap                 ! displacement generation or IFC matrix reconstruction

na nb nc                  ! specify the dimensions of the supercell to be created

cutoff[nm/-integer] ! a force cutoff distance. Positive: a distance in nm; Negative -n: n-th neighbors is automatically

bash

thirdorder_vasp.py sow 4 4 4 -3



2. Self-consistent calculation of vasp.

bashfor i in 3RD.POSCAR.*;do  s=$(echo$i|cut -d"." -f3) &&  d=job-$s && mkdir$d &&  cp $i$d/POSCAR &&  cp ~/vaspinputs/INCAR ~/vaspinputs/POTCAR ~/vaspinputs/KPOINTS $d&& cp ~/vaspinputs/runvasp.sh$d &&  (cd \$d && qsub runvasp.sh)done

3. post-process vasprun.xml files.

Some time later, after all these jobs have finished successfully, we only need to feed all the vasprun.xml files in the right order to thirdorder_vasp.py, this time in reap mode:

bash

find job* -name vasprun.xml|sort -n|thirdorder_vasp.py reap 4 4 4 -3



If everything goes according to plan, a FORCE_CONSTANTS_3RD file will be created at the end of this run. Naturally, it is important to choose the same parameters for the sow and reap steps.

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