[QE-users] difference in the order of k/q points with pw.x and ph.x

[Pietro Delugas]

Hi Hari 

They are generated by two different routines and probably with two different algorithms.  
Why are you worried about their ordering ? 

they are two different things. 

One is a MP mesh used to estimate integrals of periodic functions in the Brillouin Zone exploiting phase cancelations;   they are used all together to make an SCF calculation.
 
 The other one is a uniform grid of q points at each one of which to compute independently a dynamical matrix using all k points (plus others) of the previous list.  Then taken  all together the dynamical matrices  form the Fourier transform of the interatomic force constants in a 6X6X4 supercell.  

Regards - Pietro 




Sent from Mail for Windows 10

From: Hari Paudyal
Sent: Thursday, August 6, 2020 4:00 PM
To: Quantum Espresso users Forum
Subject: [QE-users] difference in the order of k/q points with pw.x and ph.x

Hi all,

I am doing a phonon calculation of a trigonal system with SG 164. I noticed that the order of the k (q) points printed from pw.x  and ph.x is different for the same k (q) grids.

my inputs/outputs are as the following:
pw.x input                                           ph.x input
K_POINTS {automatic}                        ldisp = .true.
6 6 4 0 0 0                                            nq1 = 6, nq2 = 6, nq3 = 4

pw.x output
     number of k points=    24  Marzari-Vanderbilt smearing, width (Ry)=  0.0200
                       cart. coord. in units 2pi/alat
        k(    1) = (   0.0000000   0.0000000   0.0000000), wk =   0.0138889
        k(    2) = (   0.0000000   0.0000000   0.1707981), wk =   0.0277778
        k(    3) = (   0.0000000   0.0000000  -0.3415962), wk =   0.0138889
        k(    4) = (   0.0000000   0.1924501   0.0000000), wk =   0.0833333
        k(    5) = (   0.0000000   0.1924501   0.1707981), wk =   0.0833333
        k(    6) = (   0.0000000   0.1924501  -0.3415962), wk =   0.0833333
        k(    7) = (   0.0000000   0.3849002   0.0000000), wk =   0.0833333
        k(    8) = (   0.0000000   0.3849002   0.1707981), wk =   0.0833333
        k(    9) = (   0.0000000   0.3849002  -0.3415962), wk =   0.0833333
        k(   10) = (   0.0000000  -0.5773503   0.0000000), wk =   0.0416667
        k(   11) = (   0.0000000  -0.5773503   0.1707981), wk =   0.0833333
        k(   12) = (   0.0000000  -0.5773503  -0.3415962), wk =   0.0416667
        k(   13) = (   0.1666667   0.2886751   0.0000000), wk =   0.0833333
        k(   14) = (   0.1666667   0.2886751   0.1707981), wk =   0.1666667
        k(   15) = (   0.1666667   0.2886751  -0.3415962), wk =   0.0833333
        k(   16) = (   0.1666667   0.4811252   0.0000000), wk =   0.1666667
        k(   17) = (   0.1666667   0.4811252   0.1707981), wk =   0.1666667
        k(   18) = (   0.1666667   0.4811252  -0.3415962), wk =   0.1666667
        k(   19) = (   0.3333333   0.5773503   0.0000000), wk =   0.0277778
        k(   20) = (   0.3333333   0.5773503   0.1707981), wk =   0.0555556
        k(   21) = (   0.3333333   0.5773503  -0.3415962), wk =   0.0277778
        k(   22) = (   0.0000000   0.1924501  -0.1707981), wk =   0.0833333
        k(   23) = (   0.0000000   0.3849002  -0.1707981), wk =   0.0833333
        k(   24) = (  -0.1666667   0.4811252  -0.1707981), wk =   0.1666667

ph.x output
     Dynamical matrices for ( 6, 6, 4)  uniform grid of q-points
     (  24 q-points):
       N         xq(1)         xq(2)         xq(3) 
       1   0.000000000   0.000000000   0.000000000
       2   0.000000000   0.000000000   0.170798095
       3   0.000000000   0.000000000  -0.341596190
       4   0.000000000   0.192450090   0.000000000
       5   0.000000000   0.192450090   0.170798095
       6   0.000000000   0.192450090  -0.341596190
       7   0.000000000   0.192450090  -0.170798095
       8   0.000000000   0.384900179   0.000000000
       9   0.000000000   0.384900179   0.170798095
      10   0.000000000   0.384900179  -0.341596190
      11   0.000000000   0.384900179  -0.170798095
      12   0.000000000  -0.577350269   0.000000000
      13   0.000000000  -0.577350269   0.170798095
      14   0.000000000  -0.577350269  -0.341596190
      15   0.166666667   0.288675135   0.000000000
      16   0.166666667   0.288675135   0.170798095
      17   0.166666667   0.288675135  -0.341596190
      18   0.166666667   0.481125224   0.000000000
      19   0.166666667   0.481125224   0.170798095
      20   0.166666667   0.481125224  -0.341596190
      21   0.166666667   0.481125224  -0.170798095
      22   0.333333333   0.577350269   0.000000000
      23   0.333333333   0.577350269   0.170798095
      24   0.333333333   0.577350269  -0.341596190

For example, you can see the 7th point from pw.x is the 8th point from ph.x and so on.

Any suggestions and explanations are highly appreciated.

Sincerely,
Hari Paudyal

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