Yambo Community Forum

Hi,
I just finished the tutorial about GW calculation in hBN, and I want to try this example in SiC example.
Well, in converging test of BndsRnXp and NGsBlkXp, I did an automated .sh file to create new input files,
and it did its job well, in the same sh file, I start the calculations,
first the BndsRnXp don't change in the report .qp files, all stays the same at 10, while NGsBlkXp changes.


input

HF_and_locXC # [R XX] Hartree-Fock Self-energy and Vxc
ppa # [R Xp] Plasmon Pole Approximation
gw0 # [R GW] GoWo Quasiparticle energy levels
em1d # [R Xd] Dynamical Inverse Dielectric Matrix
EXXRLvcs= 40 Ry # [XX] Exchange RL components
Chimod= "" # [X] IP/Hartree/ALDA/LRC/BSfxc
% BndsRnXp
1 | 20| # [Xp] Polarization function bands
%
NGsBlkXp= 1 Ry # [Xp] Response block size
% LongDrXp
1.000000 | 0.000000 | 0.000000 | # [Xp] [cc] Electric Field
%
PPAPntXp= 27.21138 eV # [Xp] PPA imaginary energy
% GbndRnge
1 | 10 | # [GW] G[W] bands range
%
GDamping= 0.10000 eV # [GW] G[W] damping
dScStep= 0.10000 eV # [GW] Energy step to evaluate Z factors
DysSolver= "n" # [GW] Dyson Equation solver ("n","s","g")
%QPkrange # [GW] QP generalized Kpoint/Band indices
30| 30| 4|5|
%

Output

# .-Input file : 20_1.in
# | em1d # [R Xd] Dynamical Inverse Dielectric Matrix
# | ppa # [R Xp] Plasmon Pole Approximation
# | HF_and_locXC # [R XX] Hartree-Fock Self-energy and Vxc
# | gw0 # [R GW] GoWo Quasiparticle energy levels
# | BoseTemp= 0.02585 eV # Bosonic Temperature
# | FFTGvecs= 6471 RL # [FFT] Plane-waves
# | X_all_q_CPU= "4.4.1.1" # [PARALLEL] CPUs for each role
# | X_all_q_ROLEs= "c.v.k.q" # [PARALLEL] CPUs roles (q,k,c,v)
# | SE_CPU= "4.2.2" # [PARALLEL] CPUs for each role
# | SE_ROLEs= "b.qp.q" # [PARALLEL] CPUs roles (q,qp,b)
# | EXXRLvcs= 40 Ry # [XX] Exchange RL components
# | Chimod= "" # [X] IP/Hartree/ALDA/LRC/BSfxc
# | % BndsRnXp
# | 1 | 10 | # [Xp] Polarization function bands
# | %
# | NGsBlkXp= 1 Ry # [Xp] Response block size
# | % LongDrXp
# | 0.1000E-4 | 0.000 | 0.000 | # [Xp] [cc] Electric Field
# | %
# | PPAPntXp= 27.21138 eV # [Xp] PPA imaginary energy
# | % GbndRnge
# | 1 | 10 | # [GW] G[W] bands range
# | %
# | GDamping= 0.10000 eV # [GW] G[W] damping
# | dScStep= 0.10000 eV # [GW] Energy step to evaluate Z factors
# | DysSolver= "n" # [GW] Dyson Equation solver ("n","s","g")
# | %QPkrange # [GW] QP generalized Kpoint/Band indices
# | 30| 30| 4| 5|
# | %




Similary probleme found in the same tutorial, when I do NGsBlkXp= 5, always reports NGsBlkXp=6. I don t know why.

I use yambo 4.1.2

Dear S. Ayoub,
Some possible explanations:
1) BndsRnXp. Check how many bands do you have calculated in the nscf calculations. If in the databases you have 10 bands you can't ask for more. You can find this information at the beginning of the report file. In this case you need to calculate more empty bands.
2) NGsBlkXp: have you specified 5 Ry, or just 5? If they are RL yambo consider the integer number needed to close the G vector shells. You can also check in the report if the ndb.pp is read form a previous calculations, in the report you have the header of the databases and you can check if it is indicated RD (so it is read) or WR, so it is calculated and written.

Best,

Daniele

Thank you so much Dr.Daniele
Your answer helped me a lot.
appreciate it

Dear all,

How many parameters do I need to converge for BSE optical absorption calculations? (I'm not planing to do full GW calculations instead will correct the QP energies via scissor operator from experimental results)
Do I need the convergence testing for NGsBlkXs, BndsRnXs and GbndRnge (GW calculations?)

Nevertheless, I am certain that following parameters will need convergence!
BSEBands, BSENGblk and BSENGexx.

And finally what is the difference between NGsBlkXs, BndsRnXs and NGsBlkXp, BndsRnXp .

Regards,
Haseeb Ahmad,
LUMS Pakistan

Dear Haseeb,

Do I need the convergence testing for NGsBlkXs, BndsRnXs and GbndRnge (GW calculations?)

You need to converge NGsBlkXs, BndsRnXs (static screening) while GbndRnge it is not a variable for BSE but just for GW (number of bands in GW summation).

Nevertheless, I am certain that following parameters will need convergence!
BSEBands, BSENGblk and BSENGexx.

Sure, these are the bands entering in the BSE matrix, and G vector in the kernel. Note that BSENGblk cannot be larger than NGsBlkXs.

And finally what is the difference between NGsBlkXs, BndsRnXs and NGsBlkXp, BndsRnXp .

Same meaning, bands and G vector in the response function (Xs and Xp): Xs is for a static screening (omega=0) that you need for BSE while Xp is for the dynamical screening in Plasmon Pole approximation needed for GW. Note that if you have already calculated the screening in plasmon pole approximation in GW you do not need to recalculate it for the BSE as yambo can read the omega=0 component for the Xp run.

In any case I suggest you to have a look to a step-by-step tutorial in order to learn the procedure and meaning of the variable:
http://www.yambo-code.org/wiki/index.ph ... =Tutorials

Best,
Daniele

Thank you very much, dear Daniele.

Dear Daniele,

Indeed I'm following the tutorials to learn about the Yambo. I have one more follow up question!

Should I run (or can I run ) yambo -b and yambo -o b -k sex -y h run-levels instead of yambo -x -p p -g n, to check convergence quickly for BndsRnXs and NGsBlkXs ? by plotting the optical spectra each time!
(
% BndsRnXs
1 | 24 | # [Xs] Polarization function bands
%
NGsBlkXs= 1
)
And like in BSEBands can I reduce the number of bands in BndsRnXs to include just close to Fermi? In my case occupied bands are 16. Can I take initially 12-18 and later check convergence of it as it is taking a lot of time for BndsRnXs and NGsBlkXs convergence with including all occupied bands! And Can I take equal values for BndsRnXs and BSEBands?

Many thanks.
From,
Haseeb Ahmad,
LUMS, Pakistan

Dear Haseeb,
BndsRnXs is for a static screening (BSE) while activates BndsRnXp that is for dynamical screening needed for a GW calculation, as it contains also the w=0 screening it can be anyway read by yambo to build the BSE kernel.
While usually in the BSE (BSEBands) a certain number of bands across Fermi is enough, in order to converge the screening you need more bands as there is a closure relation inserted \sum |n><n|=1
Briefly, the number of bands in the screening BndsRnXs and BSEBands requires a different number of bands and the convergence can be checked independently.
If you are not interested in GW correction you do not need to calculate dynamical screening (yambo -p p) so you can converge BndsRnXs directly (this will save a lot of computer time).

Best,
Daniele

Thanks again. To be sure, you mean that I should do only yambo -x -g n and not
yambo -x -p p -g n, correct? (If I don't want GW correction). Moreover,

yambo -x -g n will create BndsRnXd and NGsBlkXd, and then I should check the convergence for these two and use the same converged values for NGsBlkXs and BndsRnXs in yambo -b static screening. Is this correct way?

Regards,
Haseeb Ahmad,
LUMS, Lahore,
Pakistan.

Dear Haseeb,

yambo -x -p p -g n, correct? (If I don't want GW correction).

No, if you are not interested in calculating GW correction you can totally skip this step and assign a scissor directly in the BSE runlevel.

yambo -x -g n will create BndsRnXd and NGsBlkXd, and then I should check the convergence for these two and use the same converged values for NGsBlkXs and BndsRnXs in yambo -b static screening. Is this correct way?

No, yambo -x -g n it is meant for a GW calculation in full frequency which is very cumbersome. Again you do not need it if you do not want the QP gap. For the BSE you need to converge NGsBlkXs and BndsRnXs in yambo -b or better, to see the impact in the BSE spectrum jointly yambo -b -k sex -y h

Best,
Daniele