[CP2K-user] [CP2K:21810] Phonon Calculations in CP2K

[Ashley Dickson]

Hello everyone, 

I'm unsure if this is the right place to post this issue as I am using 
phonopy to generate phonons with CP2K, however I thought I might have a bit 
more luck finding someone with experience using phonopy specifically with 
CP2K. The issue I'm having is large negative phonon modes, and large drift 
force reported by phonopy in the y direction (~0.25 eV/A). I know that I 
shouldn't be getting negative modes as my structure is certainly 
dynamically stable. my workflow is as follows:

phonopy --cp2k -d --dim="6 6 2" -c energy.inp 

for i in energy-supercell-*; do
    bn=${i%.*}  # Remove file extension
    num=${bn#*supercell-}  # Extract the number after 'energy-supercell-'

    if [[ -z ${num} ]]; then
        continue
    fi
    dir="$num"

    if [[ -d $dir ]]; then
        echo "Skipping: Directory $dir already exists."
        continue  # Skip to the next iteration instead of exiting
    fi

    mkdir "$dir"

    mv "$i" "$dir/energy.inp"
  #  if [[ "$dir" != "001" ]]; then # Keep Wavefunction file from first 
simulation to make others quicker
 #       cp 001/MIN-supercell-001-RESTART.wfn 
"$dir/MIN-supercell-$num-RESTART.wfn"
#    fi

    cd "$dir"
    srun cp2k.psmp -i energy.inp -o result.out
    cd ../

done

phonopy --cp2k -f $(for i in {1..13}; do printf 
"%03d/MIN-supercell-%03d-forces-1_0.xyz " $i $i; done)

phonopy --cp2k -c energy.inp -p -s --dim="6 6 2" --band " 0.0 0.0 0.0  0.0 
0.0 0.5  0.0 0.5 0.5  0.0 0.5 0.0  0.5 0.5 0.0  0.5 0.0 0.0  0.5 0.0 0.5 
 0.5 0.5 0.5" --mesh 41 41 41


I have tried various supercell sizes, and have found that 4x4x2 should be 
more than converged enough. My energy.inp file has the coordinates of the 
relaxed unitcell printed as follows:
    &CELL
      A 3.870961 0 0
      B 0 3.9540005 0
      C 0 0 11.8602555
                PERIODIC XYZ
    &END CELL
   &COORD
Ba 1.9354787033 1.9770037827 9.6771343800
Ba 1.9354787999 1.9770022809 2.1442401159
Y 1.9354802394 1.9770060545 5.8953066752
Cu -0.0000006631 0.0000091908 7.6100822750
Cu -0.0000006426 0.0000055768 4.1724491018
Cu -0.0000078256 0.0000008848 -0.0048129326
O -0.0000004062 1.9770007276 -0.0014139445
O 1.9354801904 0.0000011797 7.3249015553
O 1.9354801707 0.0000009008 4.4580654293
O -0.0000001259 1.9770034877 7.3279693035
O -0.0000001304 1.9770024288 4.4553471390
O -0.0000006180 0.0000004257 9.9643054004
O -0.0000006737 0.0000003017 1.8887411088
      &END COORD

My geometry has been relaxed in a 6x6x2 supercell, with an RMS_FORCE 
setting of 1e-8 with the CELL_OPT method. The sum of atomic forces at the 
end lines up with this. I have converged my plane wave cutoff and relative 
plane wave cutoff (how converged does this need to be?). I worry it may be 
an issue with negative coordinates in the unit cell, however the periodic 
XYZ command should wrap these as I understand? 

If anyone has any suggestions as to why my phonons look quite bad I'd be 
very thankful.

Thanks in advance 
Ashley 

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