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

[xirainbow]

Dear all:

I have *four* little question about q point in ph.x and I use quantum
espresso 4.0.4.

*Question one: *How to write the input file of ph.x to get phonon dispersion
along a special line.
                       For example, 10 q-points from Gama(0 0 0) to M(0.5 0
0) in graphene?

In the output file of ph.x for only one q point, it write :
"
*      ...........*
*      Diagonalizing the dynamical matrix*
*      q = (    0.501273548   0.501273548   0.501273548 ) *
*      ...........*
"
*Question two:* What is the unit of q point?

I tried two kinds to specify the q point in input file.
One is :
"
*      ............*
*      ldisp = .true.,*
*      nq1 = 4 ,*
*      nq2 = 4 ,*
*      nq3 = 4 ,*
*      iq1 = 4 ,*
*      iq2 = 2 ,*
*      iq3 = 2 ,*
*      ............*
"
Then I get the following output:
"
*      Dynamical matrices for ( 4, 4, 4,) uniform grid of q-points*
*      with only ( 4, 2, 2,) point requested*
*      (   1q-points):*
*      N       xq(1)       xq(2)       xq(3) *
*      1     0.50000     0.50000     0.50000 "*
*      Calculation of q =   0.5000  0.5000  0.5000*
*
*
*      reciprocal axes: (cart. coord. in units 2 pi/a_0)*
*      b(1) = (  1.000000 -1.000000  0.000000 )  *
*      b(2) = (  0.000000  1.000000  1.742637 )  *
*      b(3) = ( -1.000000  0.000000  1.742637 ) *
"
*Question three:* Why                    *q=   0.5  0.5  0.5?*
                      I think it should be *q= -0.5  0.5  0.8713185.*

The other method to specify q point in input file is as below:
"
*       .......*
*      ldisp = .false.,*
*       .......*
*       /*
*      0.5000000 -0.5000000 0.8713186 *
"
Then I get the following result:
"
*      reciprocal axes: (cart. coord. in units 2 pi/a_0)*
*      b(1) = (  1.000000 -1.000000  0.000000 )  *
*      b(2) = (  0.000000  1.000000  1.742637 )  *
*      b(3) = ( -1.000000  0.000000  1.742637 )  *
*
*
*      Diagonalizing the dynamical matrix*
*      q = (    0.500000000  -0.500000000   0.871318600 ) *
"
*Question four: Is unit of q point for "ldisp = .true." and "ldisp =
.false." the same? *
*
*
*Thanks in advance：）*
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