[Pw_forum] What is the unit of q point in ph.x output file?

[xirainbow]

Dear developers:
I found a confusing thing.
*Maybe it is a bug.*

I try ph.x in quantum espresso 4.2.
input file:
"
*      &INPUTPH*
*      ............*
*      ldisp = .true.,*
*      nq1 = 4 ,*
*      nq2 = 4 ,*
*      nq3 = 4 ,*
*      ............*
"
output file:
"
*     reciprocal axes: (cart. coord. in units 2 pi/a_0)*
*               b(1) = (  1.0000 -1.0000  0.0000 )  *
*               b(2) = (  0.0000  1.0000  1.7426 )  *
*               b(3) = ( -1.0000  0.0000  1.7426 ) *

*     Dynamical matrices for ( 4, 4, 4,)  uniform grid of q-points*
*     (  13q-points):*
*       N         xq(1)         xq(2)         xq(3) *
*       1   0.000000000   0.000000000   0.000000000*
*       2  -0.250000000   0.000000000   0.435659282*
*       3   0.500000000   0.000000000  -0.871318563*
*       4  -0.250000000   0.250000000   0.871318563*
*       5   0.500000000   0.250000000  -0.435659282*
*       6   0.250000000   0.250000000   0.000000000*
*       7   0.500000000  -0.500000000  -1.742637127*
*       8   0.000000000   0.000000000   0.871318563*
*       9   0.750000000   0.000000000  -0.435659282*
*      10   0.500000000   0.000000000   0.000000000*
*      11   0.750000000  -0.750000000  -1.742637127*
*      12   0.500000000  -0.500000000  -0.871318563*
*      13   0.000000000   0.000000000  -1.742637127*
"
I can understand the above output information.

And I try another input method:
"
*      &INPUTPH*
*      ............*
*      ldisp = .true.,*
*      nq1 = 4 ,*
*      nq2 = 4 ,*
*      nq3 = 4 ,*
*      iq1 = 4 ,*
*      iq2 = 2 ,*
*      iq3 = 2 ,*
*      ............*
"
output file:
"
*     reciprocal axes: (cart. coord. in units 2 pi/a_0)*
*               b(1) = (  1.0000 -1.0000  0.0000 )  *
*               b(2) = (  0.0000  1.0000  1.7426 )  *
*               b(3) = ( -1.0000  0.0000  1.7426 ) *
*
*
*    Computing dynamical matrix for *
*    q = (   0.5000000   0.5000000   0.5000000 )*

"
Howver, I failed to understand the *    q = (   0.5000000   0.5000000
0.5000000 )*.
*
*
*"q = (   0.5000000   0.5000000   0.5000000 )" *does not appear in the 13 q
points:
*
     Dynamical matrices for ( 4, 4, 4,)  uniform grid of q-points
     (  13q-points):
       N         xq(1)         xq(2)         xq(3)
       1   0.000000000   0.000000000   0.000000000
       2  -0.250000000   0.000000000   0.435659282
       3   0.500000000   0.000000000  -0.871318563
       4  -0.250000000   0.250000000   0.871318563
       5   0.500000000   0.250000000  -0.435659282
       6   0.250000000   0.250000000   0.000000000
       7   0.500000000  -0.500000000  -1.742637127
       8   0.000000000   0.000000000   0.871318563
       9   0.750000000   0.000000000  -0.435659282
      10   0.500000000   0.000000000   0.000000000
      11   0.750000000  -0.750000000  -1.742637127
      12   0.500000000  -0.500000000  -0.871318563
      13   0.000000000   0.000000000  -1.742637127
*
*Does is a bug?*

Bye the way, do all these q points are given in the *(cart. coord. in units
2 pi/a_0)*?


-- 
____________________________________
Hui Wang
School of physics, Nankai University, Tianjin, China
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