[Pw_forum] parallelization of phonon calculations

[Torstein Fjermestad]

 Dear all,

 I am planing to do a phonon calculation on a zeolite structure. The 
 unit cell contains 37 atoms, the space group is P1, and the number of 
 irreducible representations is therefore 3*37=111. Naturally I would 
 like to parallelize this calculation as efficiently as possible.

 From the documentation of the Quantum Espresso web page I see that the 
 irreducible representations can be grouped into "images" that can be 
 computed largely independently. The following example is given:

 mpirun -np 64 ph.x -nimage 8 -npool 2 ...

 After a slight modification, I executed the following command line:

 mpirun -np 256 -npernode 8 ph.x -nimage 16 < struct0-phonon.inp > 
 struct0-phonon.out


 The calculation terminates normally, but the result is not what I 
 expected. Almost at the beginning of the output file the following it 
 printed:

      Atomic displacements:
      There are 111 irreducible representations

      Representation     1      1 modes - To be done

      Representation     2      1 modes - To be done

      Representation     3      1 modes - To be done

      Representation     4      1 modes - To be done

      Representation     5      1 modes - To be done

      Representation     6      1 modes - To be done

      Representation     7      1 modes - Not done in this run

      Representation     8      1 modes - Not done in this run

      Representation     9      1 modes - Not done in this run

 -------------------------------------------------------------
 The message "Not done in this run" is printed for Representation 7 to 
 111.

 Towards the end of the output file the frequencies are printed. 
 Frequencies 1 to 6 are slightly negative, frequencies 7 to 105 are 
 virtually zero, and frequencies 106 to 111 are slightly positive.

 The first and last part of the mentioned output section are shown 
 below:


      omega( 1) =      -7.228419 [THz] =    -241.114112 [cm-1]
      omega( 2) =      -7.052563 [THz] =    -235.248188 [cm-1]
      omega( 3) =      -6.661820 [THz] =    -222.214395 [cm-1]
      omega( 4) =      -6.390946 [THz] =    -213.179028 [cm-1]
      omega( 5) =      -6.252886 [THz] =    -208.573825 [cm-1]
      omega( 6) =      -5.895227 [THz] =    -196.643621 [cm-1]
      omega( 7) =      -0.000001 [THz] =      -0.000019 [cm-1]
      omega( 8) =      -0.000001 [THz] =      -0.000018 [cm-1]
      omega( 9) =      -0.000001 [THz] =      -0.000018 [cm-1]
      omega(10) =       0.000000 [THz] =      -0.000017 [cm-1]
      omega(11) =       0.000000 [THz] =      -0.000017 [cm-1]
      omega(12) =       0.000000 [THz] =      -0.000015 [cm-1]


      omega(98) =       0.000000 [THz] =       0.000014 [cm-1]
      omega(99) =       0.000000 [THz] =       0.000014 [cm-1]
      omega(**) =       0.000000 [THz] =       0.000015 [cm-1]
      omega(**) =       0.000000 [THz] =       0.000016 [cm-1]
      omega(**) =       0.000000 [THz] =       0.000016 [cm-1]
      omega(**) =       0.000000 [THz] =       0.000016 [cm-1]
      omega(**) =       0.000000 [THz] =       0.000016 [cm-1]
      omega(**) =       0.000001 [THz] =       0.000017 [cm-1]
      omega(**) =      16.552716 [THz] =     552.139187 [cm-1]
      omega(**) =      16.683450 [THz] =     556.499976 [cm-1]
      omega(**) =      17.480012 [THz] =     583.070434 [cm-1]
      omega(**) =      17.635841 [THz] =     588.268333 [cm-1]
      omega(**) =      17.837822 [THz] =     595.005680 [cm-1]
      omega(**) =      18.630530 [THz] =     621.447600 [cm-1]
  
 **************************************************************************

 I have a feeling that I have severely misunderstood some important 
 concepts. I would therefore appreciate if someone could give an 
 explanation on how to correctly perform a parallel phonon calculation.

 Thank you very much in advance for your help.

 Yours sincerely,

 Torstein Fjermestad
 University of Oslo
 Norway