EPW Forum

This problem seems to continue for me.

I updated the input so that it looks as follows.
On a separte note, I ran all the Examples in the EPW directory and they completed without error.
I could use help with figuring out this issue.


--
&inputepw
prefix = 'gaas'
amass(1) = 69.72300
amass(2) = 74.92160
outdir = './'

! ephwrite = .true.

epbwrite = .false.
epbread = .false.
epwwrite = .false.
epwread = .true.

elph = .true.
kmaps = .true.
etf_mem = 1

nbndsub = 12
nbndskip = 0

dis_win_max = 29
dis_froz_max= 14
dis_froz_min= -8

restart = .true.
restart_freq= 10000

wannierize = .false.
lpolar = .true.
num_iter = 5000
iprint = 2
proj(1) = 'random'
proj(2) = 'As:sp3'

! efermi_read = .false.
! fermi_energy= 5.4304

elecselfen = .true.
phonselfen = .false.

band_plot = .true.
parallel_k = .true.
parallel_q = .false.

fsthick = 25
eptemp = 300.d0
degaussw = 0.010

dvscf_dir = '../phonons/save'
filukk = './gaas.ukk'
filkf = './LGX500kpts.pwscf'
! filqf = '/u/ntandon/source/kpaths_FCC/LGX-100q.pwscf'
! filkf = '/u/ntandon/source/kpaths_FCC/LGX-25K.pwscf'

nk1 = 6
nk2 = 6
nk3 = 6

nq1 = 6
nq2 = 6
nq3 = 6

! nkf1 = 20
! nkf2 = 20
! nkf3 = 20
!
! nqf1 = 50
! nqf2 = 50
! nqf3 = 50

! rand_k = .true.
! rand_nk = 8000

!mp_mesh_k = .true.
rand_q = .true.
rand_nq = 1000000

/
16 cartesian
0.0000000 0.0000000 0.0000000 0.0092593
-0.1666667 0.1666667 -0.1666667 0.0740741
-0.3333333 0.3333333 -0.3333333 0.0740741
0.5000000 -0.5000000 0.5000000 0.0370370
0.0000000 0.3333333 0.0000000 0.0555556
-0.1666667 0.5000000 -0.1666667 0.2222222
0.6666667 -0.3333333 0.6666667 0.2222222
0.5000000 -0.1666667 0.5000000 0.2222222
0.3333333 0.0000000 0.3333333 0.1111111
0.0000000 0.6666667 0.0000000 0.0555556
0.8333333 -0.1666667 0.8333333 0.2222222
0.6666667 -0.0000000 0.6666667 0.1111111
0.0000000 -1.0000000 0.0000000 0.0277778
0.6666667 -0.3333333 1.0000000 0.2222222
0.5000000 -0.1666667 0.8333333 0.2222222
-0.3333333 -1.0000000 0.0000000 0.1111111


Thanks and regards,

Nandan.

Hello,

Except from the fact that I would use something like only
proj(1) = 'Ga:sp3'

I never use "random" projection as it is typically quite bad.

How fast are your wannier function converging (from gaas.wout file) ?

Are all the decay.X files correctly decaying ?

Apart from this, I do not see anything else that seems wrong.

Best wishes,
Samuel

Hi Samuel,

I finally finished some more tests but my results are still not as expected.

I tested two cases with different number of Wannier functions: https://drive.google.com/file/d/1CU89Zz ... sp=sharing
The decay of H and dynmat in both cases is almost identical. The decay of the electronic part is very different but better for the basis of 8 Wannier functions.

In both cases I still observe my original problem of Im(Sigma) values increases by order of magnitude for grids from 1x10^5 to 1x10^6.

==================
8 Wannier functions
==================
1.begin projections
Ga:sp3
As:sp3
end projections
num_wann 8
iprint 2
dis_win_min -1000.000
dis_win_max 20.000
dis_froz_min -1000.000
dis_froz_max 12.000
num_iter 5000
----------------------------------------

==================
12 Wannier functions
==================
2. begin projections
random
Ga:sp3
As:sp3
end projections
num_wann 12
iprint 2
dis_win_min -1000.000
dis_win_max 32.000
dis_froz_min -1000.000
dis_froz_max 15.000
num_iter 5000
dis_num_iter = 2000
-----------------------------------------------

In both cases the final interpolated bandstructures are quite similar and look as expected.

After your last email I realised that the disentanglement procedure was not converging earlier, so I had
to tweak that to get convergence.

O_D= 0.2950029 O_OD= 5.2506663 O_TOT= 21.4623126 <-- SPRD 8 Wann
5000 -0.355E-14 0.0000000600 21.4623126405 94.39 <-- CONV 8 Wann


O_D= 0.0847029 O_OD= 4.4732052 O_TOT= 23.2620467 <-- SPRD 12 Wann
5000 -0.320E-13 0.0000010973 23.2620466887 645.97 <-- CONV 12 Wann



Nandan.

Dear Nandan,

You need to plot the decays on a log scale (on the y-axis). Also dont use line but just points.

You should get that for large distance (large R), the decay should be 10^-5 or 10^-6.

For the plot you show, I cannot see that since it is a linear scale.

Also what is the spread on each atoms ?
The total spread seems quite small so I guess it is fine.
Make sure that the different WF center follow the symmetry you expect. The spread for symmetry equivalent WF should be the same.

Best wishes,
Samuel

Hi Samuel,

I have done the calculation again from scratch and now the decay files are plotted with log scale.
They seem well converged. The electronic self-energy seems well converged up to a fine
grid of 80x80x80 q-points. I think the Wannier functions are pretty good and convergences in
the Wannier basis are reasonable.

https://drive.google.com/open?id=1yX1a1 ... rpqQjUlPO-

Again comparing two basis sets of 8 and 12 Wannier functions.

The spread for 8 Wann functions:
Final State
WF centre and spread 1 ( 0.242355, 0.242355, 0.242355 ) 3.44113417
WF centre and spread 2 ( 0.242355, -0.242355, -0.242355 ) 3.44113419
WF centre and spread 3 ( -0.242355, 0.242355, -0.242355 ) 3.44113416
WF centre and spread 4 ( -0.242355, -0.242355, 0.242355 ) 3.44113416
WF centre and spread 5 ( 1.780635, 1.780635, 1.780635 ) 2.19372387
WF centre and spread 6 ( 1.780635, 0.994899, 0.994899 ) 2.19372369
WF centre and spread 7 ( 0.994899, 1.780635, 0.994899 ) 2.19372370
WF centre and spread 8 ( 0.994899, 0.994899, 1.780635 ) 2.19372370
Sum of centres and spreads ( 5.551069, 5.551069, 5.551069 ) 22.53943164

Spreads (Ang^2) Omega I = 16.526741917
================ Omega D = 0.326531509
Omega OD = 5.686157188
Final Spread (Ang^2) Omega Total = 22.539430615


=======================
Spread for 12 Wann function
=======================
Final State
WF centre and spread 1 ( 0.340648, 0.411731, 0.337860 ) 1.86326535
WF centre and spread 2 ( 0.440946, -0.432722, -0.301533 ) 1.84828970
WF centre and spread 3 ( -0.397369, 0.463047, -0.400340 ) 1.88171063
WF centre and spread 4 ( -0.302615, -0.432624, 0.442954 ) 1.84823423
WF centre and spread 5 ( 1.596391, 1.847196, 1.593193 ) 1.63024321
WF centre and spread 6 ( 2.021258, 1.104852, 1.327255 ) 1.81328200
WF centre and spread 7 ( 1.406188, 1.451997, 0.644746 ) 1.67653003
WF centre and spread 8 ( 0.644887, 1.447845, 1.405479 ) 1.66879675
WF centre and spread 9 ( -1.351863, 2.383774, 1.423447 ) 2.38704183
WF centre and spread 10 ( -1.396343, 0.340785, 1.377987 ) 2.50362522
WF centre and spread 11 ( -1.444192, 3.885355, 2.027163 ) 1.81828845
WF centre and spread 12 ( -2.942191, 2.794267, 2.614487 ) 2.63662592
Sum of centres and spreads ( -1.384255, 15.265503, 12.492698 ) 23.57593332

Spreads (Ang^2) Omega I = 18.880768911
================ Omega D = 0.058477011
Omega OD = 4.636684015
Final Spread (Ang^2) Omega Total = 23.575929937
Final State
WF centre and spread 1 ( 0.340648, 0.411731, 0.337860 ) 1.86326535
WF centre and spread 2 ( 0.440946, -0.432722, -0.301533 ) 1.84828970
WF centre and spread 3 ( -0.397369, 0.463047, -0.400340 ) 1.88171063
WF centre and spread 4 ( -0.302615, -0.432624, 0.442954 ) 1.84823423
WF centre and spread 5 ( 1.596391, 1.847196, 1.593193 ) 1.63024321
WF centre and spread 6 ( 2.021258, 1.104852, 1.327255 ) 1.81328200
WF centre and spread 7 ( 1.406188, 1.451997, 0.644746 ) 1.67653003
WF centre and spread 8 ( 0.644887, 1.447845, 1.405479 ) 1.66879675
WF centre and spread 9 ( -1.351863, 2.383774, 1.423447 ) 2.38704183
WF centre and spread 10 ( -1.396343, 0.340785, 1.377987 ) 2.50362522
WF centre and spread 11 ( -1.444192, 3.885355, 2.027163 ) 1.81828845
WF centre and spread 12 ( -2.942191, 2.794267, 2.614487 ) 2.63662592
Sum of centres and spreads ( -1.384255, 15.265503, 12.492698 ) 23.57593332

Spreads (Ang^2) Omega I = 18.880768911
================ Omega D = 0.058477011
Omega OD = 4.636684015
Final Spread (Ang^2) Omega Total = 23.575929937

Thanks and regards,

Nandan.

I have been trying to reproduce Fig.1 of the PRB paper using 700x700x700 k-grid and 100x100x100 q-grid with little success.

Looking at your input file, you are using a dense k-segment but Fig. 1 is done with a dense k-grid. Perhaps if you ran on a 200x200x200 k-grid, instead of a line segment, you get better agreement.

Vahid

Vahid Askarpour
Department of Physics and Atmospheric Science
Dalhousie University,
Halifax, NS, Canada

Vahid,

Thanks for the reply.

You are right that I have used only a few points (~500) along the LGX high symmetry path to observe the Im(Sigma). I am first
trying to optimize the integration variable defined by the q-grid, and so I am varying that from 50x50x50 to just under 100x100x100.

As long as the grid size is below 100x100x100; for example 98x98x98, I get reasonable convergence. The magnitude of Im(Sigma) correpsonds
to the one in the PRB paper. As soon as the find q-grid is increased to 100x100x100, something goes wrong and I get very large values (few order
of magnitude higher) for Im(Sigma). See the figure in the link. The density of k-points between 6.1-6.3 is small, and corresponds to the Gamma minima.

https://drive.google.com/open?id=1-Z5uA ... qumjg4G0Nl

For a denser k-path along LGX I get fairly good agreement as long as fine q-mesh is under 100x100x100. This is what I am puzzled about.

Nandan.

Nandan,

My tests with 700x700x700 k-grid and 100x100x100 q-grid finish successfully. I get the right magnitude for scattering rates/self-energy but instead of a nice thin line below 0.3eV (Gamma valley), I get scattered data.

It is likely that for larger q-grids, either your openmpi or fortran compiler is leaky. I have compiled my version with gcc/7.3.0, openmpi/3.1.0 and mkl/2018.2. I have had lots of problems with some earlier openmpi versions.

Vahid

Hi Vahid,

I would try a lower k-grid and denser q-grid instead. If you look at the Fig 5. of Comm. Phys. Comm. Volume 209, December 2016, Pages 116-133 (the EPW paper),
as the q-grid becomes denser the scatter reduces.

Thanks for the clue about the compilation issue. I have installed QE-6.2.1 this week with Intel 17.0 and OpenMPI-3.0.0 and running GaAs for a 100x100x100 grid.

Nandan.

Dear users,
can you tell me about convergence criteria , when we do the different fine qgrid calculation?
as you have said earlier, for a polar material you may need 300x300x300 qgrid , which is actually very expensive to be calculated.
Actually, I am working on PbI2, where I use qgrid 300x300x20(1.8 million qgrid). and epw is progressing with 5000 qgrid per hour, it says, it will go for 15 days approx. I am doing calculation on 112 processor, that too when I am not using enough qgrid along z axis.
can you tell me if there is any way to speed up the calculation or I can relax the convergence criteria a bit like 2 % or 3% change in (Im linewidth) with change in different higher qgrid.