[CP2K-user] [CP2K:21134] (wrong) phonons with r2SCAN

['Tyler Sterling' via cp2k]

Hi,

I am trying to model La2NiO4 using r2SCAN. I am using r2SCAN because I also 
want AFM order, which GGA typical doesn't get right. For now, I am 
calculating the "high-temperature" paramagnetic I4/mmm structure as a test. 
I am calculating phonon dispersions. This isn't the actual ground state.. 
so I do expect certain unstable modes. With PBE, the dispersions look 
reasonable with the "right" instabilities. With r2SCAN, there are 
additional unstable modes that shouldn't be unstable. I tried increasing 
CUTOFF (from 2000 Ry up to 2800 Ry!) and tried with "SCAN" 
pseudo-potentials as well as with PBE pseudo-potentials and found even more 
unstable modes! I am no expert in SCAN calculations or with CP2K, so I am 
worried I am doing something wrong in the input file. The other possibility 
is that my supercell (3x3x1 expansion of the conventional I4/mmm cell) for 
phonons (using phonopy) isn't large enough: I read somewhere that SCAN 
functionals are much more "long-ranged", so maybe I need even bigger to 
converge. 

I am attaching some minimal r2SCAN and PBE input files. These were both 
relaxed to within max-force=0.0001 Ry/Bohr before phonon calculations (all 
other relaxation params left at default values). 

I got the La basis set from the BASIS_MOLOPT_UCL file and the SCAN 
potentials from the POTENTIAL_UZH file. All other basis sets and potentials 
are from BASIS_MOLOPT and POTENTIAL respectively.

Does anyone have any idea if I am doing something wrong here? Any help is 
appreciated! Thanks :)

Ty 

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