Yambo Community Forum

Dear developers,

I am trying to use the double grid method to plot the BSE spectra of Tellurene. I manage to generate the ndb.Double_Grid (mesh of 4001 k points) file inside the SAVE directory to run with the interpolation. However, i am not sure if just only this file is enough (ndb.Double_Grid) or do i need some extra files from my previous calculation for BSE with converged parameters (e.g The screened coulomb interaction W, kernel, em1s, em1d?). If so, could you tell me which names of the files i need to look into the SAVE directory of my converged calculation?.

Another question quick questions are:
Does Double grid BSE only works with inversion?.
Does Double grid BSE accepts the QP corrections from GW calculation or it is mandatory to use the scizor operator?.

Best regards,
Kevin

Dear Kevin

yes ndb.Double_Grid must be in the SAVE directory and then you can use it for a BSE calculation using only the inversion solver

In principle you can use it also to calculate the inverse screening to build up the kernel and also for the GW calculation, but I never tested how it works

Yes you can use the ndb.QP

Maurizia

Dear Kevin

when you have the double grid I advice you to use it for all the yambo calculations GW and BSE

best
Claudio

Dear Palummo and Claudio,

Thanks for your answers!,

regards,
Kevin

Dear Yambo developers,

I am having an issue with BSE double-grid method. I am following the following tutorial:

http://www.attaccalite.com/speed-up-die ... ith-yambo/

The steps which I have done are as follows:
1: DFT (scf and nscf) with coarse k-points grid.
2: BSE spectra using inversion solver for the above k-mesh.
3: In the same directory, i.e same outdir and prefix.save folder, removing previous DFT wavefunctions only, I did another scf and nscf with dense k-grid.
4: Now, I ran p2y -w, then
5: ypp -m
Now, when I run ypp -m, it says,


Where is the SAVE?

yambo: cannot access CORE database (SAVE/*db1 and/or SAVE/*wf)

But actually ns.db1 and ns.wf is inside the SAVE folder! And I have make sure that code was compiled with netcdf. In fact ypp seems to be working with another save database but not with this double-grid database!!

Can you please identify the mistake that I am doing in these steps?

Thanking you,

Dear haseebphysics1

when you do "ypp -m" for the first time you should specify the folder
where is the folder with many-kpoints, something like
and then you should run in the folder where you have the original calculation
with the 8x8 k-points grid (in this example).

Let me know if it works.

best
Claudio

Dear Claudio, thanks for your reply!

I have understood the procedure now, and I am doing it again since I have distorted the database now! I will let you know in case of any problems.

Meanwhile can we please clarify the following things:

Q1: What does this variable means?

BZ_DbGd_Nk=0 # BZ Number of points in the double grid

Is it okay to comment it and hence not using it!

Q2: Does the double grid contains the course-grid points + dense grid points (in BZ)! Am I correct?

Q3: In step 6 of your tutorial, should I run the bse calculation again using the same bse input file with ndb.doublegrid in the SAVE folder and will it automatically use the modified k-points (double k-grid)?

Thanking and wishing you good health,

Dear Haseeb Ahmad

haseebphysics1 wrote: ↑Mon Mar 16, 2020 10:14 pm
Q1: What does this variable means?
BZ_DbGd_Nk=0 # BZ Number of points in the double grid

Is it okay to comment it and hence not using it!

I do not remember this variable, other developers will answer to this question

Q2: Does the double grid contains the course-grid points + dense grid points (in BZ)! Am I correct?

Yes

Q3: In step 6 of your tutorial, should I run the bse calculation again using the same bse input file with ndb.doublegrid in the SAVE folder and will it automatically use the modified k-points (double k-grid)?

yes, if the caculation does not start, just remove the ndb.BS* databases

best regards
Claudio

Dear Yamboers,

I already have the ndb.Double_Grid file in my SAVE directory, how to do a GW calculation? Is it sufficient to run the standard GW input script with this SAVE folder?

Regards,
Sitangshu

claudio wrote: ↑Tue Oct 23, 2018 12:31 pm Dear Kevin

when you have the double grid I advice you to use it for all the yambo calculations GW and BSE

best
Claudio

Yes, it is sufficient to run a standard GW input,
in the report you will indication about the use of the double-grid