BSE calculation- dense k-grid

[pyadav]

Dear Developers,

Can someone please help me with doing BSE calculation using a very dense k-grid, like 51x51x1 while keeping the DFT k-grid low (12x12x1)? There is a paper that has mentioned YAMBO for this purpose (PHYSICAL REVIEW B 88, 045412 (2013).

Wishes,
Pushpendra

[Daniele Varsano]

Dear Pushpendra,
I may be wrong, but in the paper you mention a large grid (51x51x1) is used.
Can you explain better what you mean by keeping the DFT k-grid low (12x12x1)?

Best,
Daniele

[pyadav]

Dear Dr. Daniele,

Maybe I misunderstood the paper mentioned above but I wanted to understand that suppose we do a ground-state calculation (scf/nscf) for k-grid 12x12x1 and use these ground state wave-functions to do the G0W0 calculation. Now if I want to calculate BSE spectra for a higher k-grid (say 51x51x1). For this hogher k-grid BSE calculation do I need to go back to DFT calculation with higher k-grid or is it possible to implement higher k-grid in YAMBO?

Thank you!

[Daniele Varsano]

Dear Pushpendra,
yes, you need to recalculate the electronic structure for a denser grid, as you need it to build your BSE matrix.

Best,
Daniele

[pyadav]

Thank you, Dr. Daniele, for the clarification.

[Zafer Kandemir]

Dear Dr. Daniele,

Maybe I misunderstood the paper mentioned above but I wanted to understand that suppose we do a ground-state calculation (scf/nscf) for k-grid 12x12x1 and use these ground state wave-functions to do the G0W0 calculation. Now if I want to calculate BSE spectra for a higher k-grid (say 51x51x1). For this hogher k-grid BSE calculation do I need to go back to DFT calculation with higher k-grid or is it possible to implement higher k-grid in YAMBO?

Thank you!

Dear Developers,

Is this calculation possible for the new version of the Yambo program?

Best regards,
Zafer

[Daniele Varsano]

Dear Zafer,

can you be more explicit on what kind of calculation you are referring?
In the previous post, the user was asking about BSE calculations using a dense grid without calculating the ground state on such grid. This is not possible.
What is possible is to speed up the calculation using a double gri method as explained here:
http://www.attaccalite.com/speed-up-die ... ith-yambo/

or via Haydock method as described here:

https://www.frontiersin.org/articles/10 ... 63946/full


Best,
Daniele

[Zafer Kandemir]

Dear Daniele,

Thank you for replying, my question is like this: For k-grid 18x18x8, a ground state calculation of a bulk structure was made, and then GW calculation was made and ndb.QP was obtained. Now I want to calculate BSE spectra for k-grid 26x26x10. This calculation is not possible, ok.
If I want to use the double grid method, I should choose k-grid:18x18x8 for scf calc. and k-grid:26x26x10 for ncsf calc. Is it possible to calculate BSE spectra by using the ndb.QP file obtained from the previous GW calculation?

Best regards,

Zafer

[Daniele Varsano]

Dear Zafer,

It is not possible to use the ndb.QP directly. You can use a scissor/stretching operator with parameters extracted from the previous calculation and apply them to the calculation with denser grid.

Best,
Daniele