[QE-developers] Incompatible FFT grid in ph.x calculation

[Xiao Zhang]

Dear QE developers,

I'm sending the email asking about an error I get from the phonon
calculations in the 6.6 version of quantum espresso. I'm trying to run
phonon calculation for 2H SiC and have the scf run finished with no
problem, but when I run phonon calculation following that, I received an
incompatible FFT grid error. This happened only with the new version of QE
while using the exact same input, QE 6.5 works fine and provides output. I
was wondering if this is something we expect? (I do realize there is one
potentially relevant tag on the release note under "fixed")

I attached one example just in case it might help: This is 2H-SiC and I
attached the input and output from scf, input and output from ph.x from
both 6.5 and 6.6. The k-points and cutoffs are reduced for quick tests, but
converged k-points and cutoffs show the same issue. The structure is
relaxed within QE, and the PP used is ONCV-PBE. I'm a bit confused why this
is seen in phonon calculation but not the scf calculation? I assumed that
if it's a problem of my input structure, I should've seen a problem in
both? Any hint or suggestions would be very helpful!

Thanks a lot!
Best!
Xiao Zhang
Department of Materials Science and Engineering
University of Michigan, Ann Arbor
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