[QE-users] Different output information in phonon calculation of 'GRID' and 'SPLIT'.

[黄志硕]

Dear all QE users,

I am calculating phonon dispersion using two modes of PH module of quantum espresso. One mode is to split total calculation into calculations of each irreducible q point (SPLIT), while the other is the GRID calculation as the demonstrated in the GRID_example, which is to take all the irreducible representations into consideration. However, the output files shows different information when I use these two method to calculate phonon frequency with the same structure and scf input. The main difference is that in the output of GRID method there is a warning shown below:
##########################################################
     Starting wfc are  267 atomic wfcs

Possibly too few bands at point    1  -0.12500   0.12500   0.12500
Possibly too few bands at point    2   0.37500  -0.37500   0.62500
Possibly too few bands at point    3  -0.37500   0.37500  -0.12500
Possibly too few bands at point    4   0.12500  -0.12500   0.37500
…
…
…
Possibly too few bands at point   87  -1.12500  -0.37500  -0.37500
Possibly too few bands at point   88  -0.62500  -0.87500   0.12500
##########################################################
While there is no such information in the output file of SPLIT method. 

The input of GRID method for each irreducible representation is shown below 
##########################################################
Phonon of K3C60
 &inputph
  tr2_ph=1.0d-17,
  prefix='K3C60',
  ldisp=.true.
  nq1=2, nq2=2, nq3=2
  start_q=2
  last_q=2
  start_irr=’irr_num’,
  last_irr=’irr_num’,
  amass(1)=12
  amass(2)=39.1
  outdir='./',
  fildyn='K3C60.dynG',
  reduce_io = .true.
 /
##########################################################
And the input of GRID method after collecting all the information of each irreducible representation is 
##########################################################
Phonon of K3
 &inputph
  tr2_ph=1.0d-17,
  prefix='K3C60',
  ldisp=.true.
  nq1=2, nq2=2, nq3=2
  recover=.true.,
  start_q=2
  last_q=2
  amass(1)=12
  amass(2)=39.1
  outdir='./',
  fildyn='K3C60.dynG',
  reduce_io = .true.
 /
##########################################################

And the input of SPLIT method is 
##########################################################
Phonon of K3C60
 &inputph
  tr2_ph=1.0d-17,
  prefix='K3C60',
  ldisp=.true.
  nq1=2, nq2=2, nq3=2
  start_q=2
  last_q=2
  amass(1)=12
  amass(2)=39.1
  outdir='./',
  fildyn='K3C60.dynG',
  reduce_io = .true.
 /
##########################################################

Why is there the difference information in the output file for the same structure and scf input? I will appreciate it if anyone could give me any information about that.

Best regards
Zhishuo Huang

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