FFT grid dimensions

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vojtech.vlcek
Posts: 5
Joined: Fri Mar 16, 2012 11:48 am

FFT grid dimensions

Post by vojtech.vlcek » Fri Mar 15, 2013 12:09 am

Dear all,

I would like to ask about a warning that appears in the log file for calculations using a sequential version of abinit 7.0.5:

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getng.F90:199:WARNING
   The second and third dimension of the FFT grid,    0    0  were imposed to be multiple of the number of processors for the FFT,    1
 For input ecut=  3.000000E+01 best grid ngfft=      36      36      36
       max ecut=  3.085668E+01

 ==== FFT mesh ====
  FFT mesh divisions ........................    36   36   36
  Augmented FFT divisions ...................    37   37   36
  FFT algorithm .............................   112
  FFT cache size ............................    16
 getmpw: optimal value of mpw=    2071


The same appears also in the parallel version, though I am not using paral_kgb option. In both cases the code does not crash and continues in the computation. If I understand correctly what is written in the log shown here, the ngfft(2) and ngfft(3) are non zero (here ngfft(2)=36 and the same for ngfft(3)). Moreover, at the end of the log I find that:

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ngfft          36      36      36

I (naively) expected that this warning should appear only if the paral_kgb=1 and if the variable npfft is not set properly. Does it mean that I made a mistake while compiling the code or what could be the reason?

Thank you in advance for any help.

Vojtech

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