EPW Forum

Dear All,

I found a problem during the wannierization of graphene.
When I run the EPW code in serial mode (without mpirun),
the wannierization procedure seems to be fine
and the resulting wannier functions are consistent with what I get by directly running wannier90 code.

However, when I use mpirun with EPW,
I get unphysically large value of Omega_I during the disentanglement procedure.
This naturally ruins the wannierization procedure so that the resulting WFs become messy.

I traced the root of the problem to the variable m_mat in the EPW code.
I found that the matrix elements of m_mat are different for serial and MPI run.
In the MPI run, the values of m_mat is huge (>1e10), whereas they are order of unity in serial run.

I am wondering if this is because of a possible bug in compute_mmn_para routine.
Here is the link of the input and pseudopotential files that I have tested the above problem.
https://drive.google.com/open?id=1rlsOeIALTF2PC-KoOma1_t6HcCt51G7l

Please check this problem is reproduced in other environments.
Thank you.

p.s. I used QE distribution 6.2.1 compiled with intel compiler 18

I found that this problem only occurs when using ultrasoft pseudopotentials.
When I run the code with the same input files but with a norm-conserving pseudo potential,
the above problem did not occur and the wannierization procedure went well.

Since I am not familiar with USPP, it is hard for me to further debug this problem.
I hope this issue will be taken care of by EPW developers.

Thank you.

Hi, ywchoi:

I am really happy to meet the colleague from Yonsei; I also graduated from Yonsei.

Returning to your question:
First of all, I think that the current version of EPW is not compatible with USPPs.

In any case, although I am not developers, I can easily find one minor bug in pw2wan90epw.f90.

Find the following line:
CALL init_us_2 (npwq, igkq, xk(1,ikp), vkb)

Then, change this line as below:
CALL init_us_2 (npwq, igkq, xktot(1,ikp), vkb)

ikp is a global k point, but xk is defined locally. Thus, we have to use xktot instead of xk.

Sincerely,

Hyungjun Lee

Dear Dr. Lee,

It is nice to meet you too.
Thank you for your comment, and it seems the problem is solved when I fixed the code according to your comment.
But, as you mentioned, I decided to use NCPP in this EPW version.

Thank you,
Young Woo Choi

Hello Hyungjun Lee,

I added your change to EPW. Thanks.

USPP is indeed not yet supported (I never found the time to finish this ).

If you have a working implementation of USPP in EPW, I would be most happy to put it inside and to credit you for it !

Best wishes,
Samuel