[CP2K-user] [CP2K:21814] Phonon Calculations in CP2K

[Ashley Dickson]

Also adding on to my previous comments, I use the following mixing approach:
   &MIXING  T
        METHOD BROYDEN_MIXING
        ALPHA 0.2
        BETA 1.5
        NBUFFER 15
      &END MIXING

Could this be responsible for any differences in convergence issues perhaps?

On Tuesday, 9 September 2025 at 15:05:55 UTC+1 Ashley Dickson wrote:

> Hi Matthias,
>
> thanks for the response. For your information I am using the finite 
> difference method here. Supposing this was the issue, how would you 
> recommend solving it? Presumably I can't explicitly freeze the orbital 
> occupations for the displaced configurations? Perhaps including the 
> wavefunction of the initial geometry as an initial guess might keep the 
> correct spin state.
>
> Also, I wonder if the anisotropic nature of YBCO is the issue here. It is 
> not strictly magnetic, although the copper chains/planes may act as such 
> and mess up the forces. Would it be beneficial to include spin in my 
> calculations maybe? 
>
> Many thanks 
> Ashley 
> On Tuesday, 9 September 2025 at 14:44:39 UTC+1 Krack, Matthias wrote:
>
>> Hi Ashley
>>
>>  
>>
>> Regarding the CP2K side, you should check if all the finite difference 
>> force calculations converged properly to equivalent (magnetic?) states 
>> during an atomic displacement. You do not report the applied computational 
>> method and I can only guess, but I would have a look at the Cu 3d 
>> occupations of the YBCO before and after an atomic displacement.
>>
>>  
>>
>> Best
>>
>>  
>>
>> Matthias
>>
>>  
>>
>> *From: *cp... at googlegroups.com <cp... at googlegroups.com> on behalf of 
>> Ashley Dickson <ashleydi... at gmail.com>
>> *Date: *Tuesday, 9 September 2025 at 12:39
>> *To: *cp2k <cp... at googlegroups.com>
>> *Subject: *[CP2K:21810] Phonon Calculations in CP2K
>>
>> 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 <(327)%20969-3035>
>> O -0.0000001304 1.9770024288 4.4553471390
>> O -0.0000006180 0.0000004257 9.9643054004
>> O -0.0000006737 0.0000003017 1.8887411088 <(888)%20741-1088>
>>       &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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>

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