EPW Forum

Hello,

please answer one question related to modeling using epx.x program for
graphene modified by hydrogen atoms. It is not clear to me how to select in the input file epx.in the values of parameters nqs{cartezian} and parameters xq(1), xq(2), xq(3) for this material.

Thank you for your reply.
Valery

Hi Valery,

I think https://docs.epw-code.org/doc/Inputs.html#nqs will help you to understand the input flags.

xq(1), xq(2), xq(3) are the phonon wavevectors of the coarse grid. Must be in the same order as prefix_q* listed in dvscf_dir. You can copy these from the beginning of the phonon output file.

If you are using the latest versions of the code, you do not need to specify them explicitly, and are calculated internally with respect to nq1, nq2, and nq3.

Best,
Hari Paudyal

Hi Hari Paudyal.

Thank you for your reply.
Please answer one more question related to modeling using epw.x program for graphene modified by hydrogen atoms. I calculated parameters xq(1), xq(2), xq(3) for this material with the program ph.x and passed it in program epw.x. Text of input file listed here. But when I ran the epw.x program, I got the answer “Error in routine epw_setup (1): coarse k-mesh needs to be strictly positive in 1st BZ stopping “.

I do not know if it is possible to simulate such systems or if I have made some mistakes.

Valery

--
&inputepw
prefix = './'
amass(1) = 12.011
amass(2) = 1.0079
outdir = './'
elph = .true.
kmaps = .false.
epbwrite = .true.
epbread = .false.
epwwrite = .true.
epwread = .false.
nbndsub = 4
nbndskip = 0
wannierize = .true.
num_iter = 300
iprint = 2
dis_win_max = 12
dis_froz_max= 7
iverbosity = 0
elecselfen = .false.
phonselfen = .true.
a2f = .true.
fsthick = 2.80284905 ! eV
eptemp = 300 ! K
degaussw = 0.1 ! eV
dvscf_dir = './'
filukk = './C2H1.ukk'
nk1 = 12
nk2 = 12
nk3 = 12
nq1 = 12
nq2 = 12
nq3 = 12
nqf1 = 20
nqf2 = 20
nqf3 = 20
nkf1 = 10
nkf2 = 10
nkf3 = 10

! The list of qpoints below must be identical
! to ../phonons/qlist.dat
/
31 cartesian
0.000000000 0.000000000 0.000000000
0.000000000 0.115470054 0.000000000
0.000000000 0.230940108 0.000000000
0.000000000 0.346410162 0.000000000
0.000000000 0.461880215 0.000000000
0.000000000 -0.577350269 0.000000000
0.100000000 0.057735027 0.000000000
0.100000000 0.173205081 0.000000000
0.100000000 0.288675135 0.000000000
0.100000000 0.404145188 0.000000000
0.100000000 0.519615242 0.000000000
0.200000000 0.115470054 0.000000000
0.200000000 0.230940108 0.000000000
0.200000000 0.346410162 0.000000000
0.200000000 0.461880215 0.000000000
0.200000000 0.577350269 0.000000000
0.200000000 0.000000000 0.000000000
0.300000000 0.173205081 0.000000000
0.300000000 0.288675135 0.000000000
0.300000000 0.404145188 0.000000000
0.300000000 0.519615242 0.000000000
0.300000000 -0.057735027 0.000000000
0.400000000 0.230940108 0.000000000
0.400000000 0.346410162 0.000000000
0.400000000 0.461880215 0.000000000
0.400000000 0.577350269 0.000000000
0.400000000 -0.115470054 0.000000000
0.400000000 0.000000000 0.000000000
-0.500000000 -0.288675135 0.000000000
-0.500000000 -0.173205081 0.000000000
-0.500000000 -0.057735027 0.000000000

Program EPW v.5.0.0 starts on 16Apr2021 at 14:37: 0
Serial version
Reading data from directory: ././.save/
IMPORTANT: XC functional enforced from input :
Exchange-correlation = PBE ( 1 4 3 4 0 0)
Any further DFT definition will be discarded
Please, verify this is what you really want
file C.pbe-rrkjus.UPF: wavefunction(s) 2S 2P renormalized
file H.pbe-rrkjus.UPF: wavefunction(s) 1S renormalized
Error in routine epw_setup (1):
coarse k-mesh needs to be strictly positive in 1st BZ
stopping ...

Dear Valery:
The q-point list should be given in Cartesian units and as Hari mentioned, its format should follow the specific form described at https://docs.epw-code.org/doc/Inputs.ht ... input-data .

Well, is there a specific reason to use the old version of EPW? I strongly suggest you to use the latest version of EPW (EPW v5.3.1).

Sincerely,

H. Lee

Dear H.Lee

Thank you for your reply. But what is wrong with these points. The points I am using are from the ph.x program and I used according to Hari recommendations in his previous letter. If the 5.0 program version is not correct and cannot do the simulation of this structure, then I will install the 5.3.1 version in the future.

Sincerely,

Valery

Dear Valery:

First, I don't know about EPW v5.0, but you might need to add the fourth column of weight as described at https://docs.epw-code.org/doc/Inputs.ht ... input-data .
I guess that even in EPW v5.0, the weights are internally ignored; so you can use the weight of 1.0 for all q points.
Second, your system is a 2D system and probably, in your scf, nscf, and ph calculations, you might use the number of grid of 1 along the kz direction.
(Could you confirm that you used the grid of "12 12 1" from your nscf and ph calculations?)

Thus, please replace the above part by the following:
Sincerely,

H. Lee

Good afternoon,

Thank you for your reply, but my problem has not yet been solved. Now I am trying to put the new version of QE-6.7 on my computer, but there are problems here. Therefore, for the time being, I work in QE-6.3. These days, I tried to solve a similar problem for SiC material, using the files that were in the examples of the program QE-6.3. The program epw.x for SiC material started to simulate when I put the largest grid with the number of points 216 (for the grid 6*6*6=216). With less number of points I got the same error as for my variant with graphene. So maybe I also need to use the exact grid with more number of points 144 (for 12*12*1 grid). If this is the case, then how do I get a grid with this number of points, because the ph.x program only gives me 63 points. I inform you that I have fulfilled all your comments made in the last letter. Maybe with QE-6.7 program everything will be easier and my problem will be solved. Excuse me for my persistence, but I am very interested in research of electron-phononon interaction in two-dimensional materials.


Respectfully,
Mishchenka Valery

Dear Mishchenka Valery:

First, I would suggest you again to use the recent version of EPW (v5.3.1) since it is much easier for me to keep track of the (potential) issues you encounter.

In addition, I would like to look at all of your inputs and outputs (scf.in, scf.out, nscf.in, nscf.out, ph.in, ph.out, epw.in, and epw.out).

Sincerely,

H. Lee

Dear H. Lee,

I received your last letter where you offer me to send input and output files obtained with program QE-6.3. However, taking into account your repeatedly stated recommendation to use EPW 5.3.1 program, I installed program QE-6.7. With its help I ran programs pw.x and ph.x for my variant of simulation with graphene and obtained satisfactory results.
However, the installation of the EPW program, which came with QE-6.7, ended unsuccessfully and a message was received in the end:

Make: *** [epw] Error 1

In the long text that accompanied the installation, I read two warnings.

The first one was:
Unable to download www.netlib.org/lapack/lapack-3.6.1.tgz.

Then I downloaded this archive and extracted it into the Lapack folder.

The second of them:
Unable to download wannier90. ......copy files located here: https://codeload.github.com/wannier-dev ... .gz/v3.1.0.

However I haven't found above mentioned files in this path.

How can I solve this problems? Thanks for the answer!

Best regards,
Mishchenka Valery.

Dear Mishchenka Valery:

Unable to download wannier90. ......copy files located here: https://codeload.github.com/wannier-dev ... .gz/v3.1.0.

I can download the file at https://codeload.github.com/wannier-dev ... .gz/v3.1.0 .
If you are using the clusters at the HPC center, you had better consult with the staffs there about the installation failure.

Sincerely,

H. Lee