G0W0 for a 2D layer

[rnanune]

Dear Yambo developers,

I would like to run G0W0 calculations for a 2D slab geometry. I performed the mean-field using PW and ran 'p2y' and 'setup'. I got the following messages during 'setup':

<---> [01] Files & I/O Directories
<---> [02] CORE Variables Setup
<---> [02.01] Unit cells
<01s> [02.02] Symmetries
<01s> [02.03] RL shells
<02s> Shells finder |####################| [100%] --(E) --(X)
<02s> [02.04] K-grid lattice
<02s> [02.05] Energies [ev] & Occupations
<02s> [03] Transferred momenta grid
<02s> [WARNING][RL indx] 2 equivalent points in the rlu grid found
<02s> [RL indx] X grid is not uniform. Gamma point only.
<02s> [04] Game Over & Game summary

I would like to ask whats the meaning of the warning above:
1) What does it mean 2 equivalent points in the rlu grid found?
2) Why is the X-grid not uniform and why do I get 'Gamma point only.'?

Thanks,
Ravindra Nanguneri
Department of Chemistry & Biochemistry
University of Notre Dame
251 Nieuwland Science Hall, Notre Dame, IN 46556
USA

[Daniele Varsano]

Dear Ravindra,
the problem here is that Yambo did not recognize the q-grid as uniform, hence it automatically switch to a gamma-point only calculation.
Check your k-point sampling in PW. Did you use an automatic grid or a grid you provided in input?
The problem can also appear if PW considered non-symmorphic symmetries, in order to avoid that you need to use the
keyword:

Code: Select all

force_symmorphic= .true.

in the system namelist both in scf and nscf calculation.

Check this, and if it does not work please provide your PW input and output.
Best,
Daniele

[rnanune]

Dear Daniele,

I used an automatic grid for the 2D slab geometry PW calculations. I tried your suggestions to set: "force_symmorphic= .true." in the namelist "system" in the SCF and NSCF input files. But I still get the message that the "X grid is not uniform" and that "2 equivalent points in the rlu grid found" when I run Yambo in setup mode:
<---> [01] Files & I/O Directories
<---> [02] CORE Variables Setup
<---> [02.01] Unit cells
<01s> [02.02] Symmetries
<01s> [02.03] RL shells
<02s> Shells finder |####################| [100%] --(E) --(X)
<02s> [02.04] K-grid lattice
<02s> [02.05] Energies [ev] & Occupations
<02s> [03] Transferred momenta grid
<02s> [WARNING][RL indx] 2 equivalent points in the rlu grid found
<02s> [RL indx] X grid is not uniform. Gamma point only.
<02s> [04] Game Over & Game summary

I am attaching my PW SCF and NSCF input and output.

Thanks,
Ravindra Nanguneri
Department of Chemistry & Biochemistry
University of Notre Dame
251 Nieuwland Science Hall, Notre Dame, IN 46556
USA

[Daniele Varsano]

Dear Ravindra,
I can't see the attached files.
Daniele

[rnanune]

Dear Daniele,

Sorry I didn't attach to my previous email. Attached are the PW scf and nscf input/output files.

Thanks,
Ravindra Nanguneri
Department of Chemistry & Biochemistry
University of Notre Dame
251 Nieuwland Science Hall, Notre Dame, IN 46556
USA

[Daniele Varsano]

Dear Ravindra,
it is not easy to spot the problem.
The only think I can see is that in your nscf.out file you have:

Code: Select all

s                        frac. trans.

it looks that fractional translations are considered and it gives the problem.
Anyway fractional translations should be disabled by the force_symmorphic keyword. I noticed that there is a "," missing, but this should not cause problem.
Try to insert the proper comma, check the overall syntax.
By the way I would not include in the input:
exxdiv_treatment = 'gygi-baldereschi'
as it is not used, and check also tif he condition in the note for the esm method in the qe input page are fulfilled.
and if not working you can try may be to write to the QE mailing list.
Or may be other people here can come with better suggestion.
Best,
Daniele

[rnanune]

Dear Daniele,

I would like to do G0W0+BSE for 2D layered systems. If Yambo finds the q-grid of the 2D system is not uniform and switches to a Gamma-point only calculation, would it be possbile to do G0W0+BSE?

Thanks,
Ravindra Nanguneri
Department of Chemistry & Biochemistry
University of Notre Dame
251 Nieuwland Science Hall, Notre Dame, IN 46556
USA

[Daniele Varsano]

Dear Ravindra,
it is possible but the results will be totally unconverged and most probably meaningless as in GW and BSE implementations integrals in the BZ are needed, which imply convergence tests on the k-point sampling.
I suugest you to write to the quantum espresso mailing list in order to spot the problem with the non symmorphic symmetries of your DFT calculation.
Best,
Daniele