EPW Forum

Dear all users,

Hello.

I calculate for superconducting parameters using QE+EPW,
My system is body-centered tetragonal structure(No. 139, ibrav=7).

I have two question, but same problem.

First,
in ph.x process, the 4 q-points are shown for 2x2x2 q-mesh.
For lambda.x calculation, when I got an weight value using kpoint.x,
the meshes are different with the q-points in ph.out file.

Q) what is fifth number in the generated file? For example, 3 in 4th low or 2 in 7th low?
Q) How can I match the q-points in ph.out and generted out file?

===================================================
In ph.out file.

Dynamical matrices for ( 2, 2, 2) uniform grid of q-points
( 4q-points):
N xq(1) xq(2) xq(3)
1 0.000000000 0.000000000 0.000000000
2 0.500000000 0.000000000 -0.146200241
3 0.500000000 -0.500000000 -0.292400482
4 0.000000000 0.000000000 -0.292400482

In generated out file from kpoints.x
8
1 0.0000000 0.0000000 0.0000000 1.00
2 0.5000000 -0.5000000 0.0000000 2.00
3 0.0000000 0.5000000 0.1462002 4.00
4 0.5000000 0.0000000 0.1462002 0.00 3
5 -0.5000000 0.0000000 0.1462002 0.00 3
6 0.0000000 -0.5000000 0.1462002 0.00 3
7 -0.5000000 0.5000000 0.2924005 0.00 2
8 0.0000000 0.0000000 0.2924005 1.00
=====================================================


Second,
In EPW calculation, there are 5 process.

for getting a phonon dispersion
1. pw.x <scf.in> scf.out
2. ph.x <ph.in> ph.out

for epw process
3. pw.x <scf.in> scf.out
4. pw.x <nscf.in> nscf.out
5. epw.x <epw.in> epw.out

In the nscf calculation, I need the nscf klist consistent with elph k-point grids.
2x2x2 q-points need 8 nscf klist(satisfying with positive k-points in 1BZ).
I used the generated klist from kpoins.x, however this klist should be positive value.

8
0.0000000 0.0000000 0.0000000
0.5000000 0.5000000 0.0000000
0.0000000 0.5000000 0.1462002
0.5000000 0.0000000 0.1462002
0.5000000 0.0000000 0.1462002
0.0000000 0.5000000 0.1462002
0.5000000 0.5000000 0.2924005
0.0000000 0.0000000 0.2924005

But, 3th and 6th low are same point. 4th and 5th also are same.
So, I need other two values.

Q ) Any good idea?

Also, could you suggest any literature or reference?



Thank you,
Myung-Chul.

--
=============================================================
Myung-Chul Jung
Ph. D student
Department of Applied Physics
Korea University, Sejong campus
2511 Sejong-ro, Sejong
30019, Republic of Korea
=============================================================

Dear Myung-Chul,

Regarding your first two questions, the q points you see in the ph.out are only the irreducible one. I checked quickly kpoints.x, and I can see the script gives you two options, 'write all k' T/F. It seems you chose T in your case, which means you get all the points in the uniform grid, and the fifth number tells you to which irreducible q point star that point belongs. If you choose F then you should get only 4 points (the irreducible ones).

Your way of getting a positive uniform grid for nscf.in is wrong because the coordinates you get from kpoints.x are cartesian. You should input your coordinates in crystal, so it would be:
0 0 0
0 0 0.5
0 0.5 0
0 0.5 0.5
0.5 0 0
0.5 0 0.5
0.5 0.5 0 .
0.5 0.5 0.5

Best
Carla

Dear Carla


Thanks for reply.
It's doing well.

Best regards,
Myung-Chul

Dear All,
how genetare kpoints for nscf in crystal coordinates?

Best Regards,
Arnie

Dear Arnie,

I think you can generate kpoints for nscf in crystal coordinates with the script in QE/wannier90/uitlity/kmesh.pl

Bests,
Xinbao