BSE

[fatimazahra]

Hi
I'm trying to calculate the dielectric fonction with BSE, I run yambo -o b -y d -K sex -b -V qp. I get the first exciton in 5.32 ev (excitation energy) but the gap energy in 3.71 eV. If , In this case, I find that the binding enrergy is negative value.
Thank you in advance

[Daniele Varsano]

Dear Fatima,
in this case the exciton it is not bound. I do not know what system you are considering, consider that also in the BSE calculations there are many variables to be converged.
Best,
Daniele

[fatimazahra]

Hi
Thank you
I am converged the variables. The system is silicon carbide two dimensional.

[muthu]

Hello all Yambo users
i want to calculate optical properties of pure tio2 and doped tio2 systems. i have gone through this conversation
(viewtopic.php?f=13&t=787). regarding BSE calculations i got one question.
i'm newbie to yambo. i do not know list of variables to be converged. so i request all to list variables that to be converged.

i post this question to equip myself so i expect answers irrelevant of and i think this post would help other newcomers.also that i thank in advance fro all replies.
i look forward for replies
thank you
*********************************
Muthu.V
Project Fellow
Dept. of Theoretical Physics
Madurai Kamraj University
**********************************

[Daniele Varsano]

Dear Muthu,
Please have a look to the tutorias on the yambo website. In particular the fantastic dimension one. If there is something unclear you post here your questions.
Best
Daniele

[muthu]

thank you Daniele Varsano for your kind reply.

firstly i have gone through tutorials you have mentioned. but before strating calculations, i want to initilize yambo so that i refered LiH tutorial. in this tutorial at first step it is given that

in the Inputs/01_init file. In the report file we notice that

G-vectors [RL space]: 1807
[wavefunctions]: 1807

whereas the Reciprocal Space shells found by yambo are

G-vector (S)hells. Format: [Snn] G`s
[S0030]: 773 [S0029]: 749 [S0028]: 725 [S0027]: 701 [S0026]: 645
[S0025]: 609 [S0024]: 561 [S0023]: 537 [S0022]: 531 [S0021]: 459
[S0020]: 411 [S0019]: 387 [S0018]: 339 [S0017]: 331 [S0016]: 307
[S0015]: 283 [S0014]: 259 [S0013]: 229 [S0012]: 181 [S0011]: 169
[S0010]: 137 [S0009]: 113 [S0008]: 89 [S0007]: 65 [S0006]: 59
[S0005]: 51 [S0004]: 27 [S0003]: 15 [S0002]: 9 [S0001]: 1

i want to do the same calculation but how to get above table. ie i can change MaxGvecs in yambo.in produced by running yambo -i -V all. but what is shell where can i get its value and control this.

and one more thing is
in yambo calculation the first parameter to be converged is MaxGvecs. is it correct?

[Daniele Varsano]

Dear Muthu,
please add your full name and affiliation in your signature, this is a rule of the forum.
In the setup run, yambo does read the KS structure generated by qe or abinit and generate the database corresponding to the g vectors and k vectors to be used in all the further runs. In the report all the KS electronic structure is reported. As you can see the first and last division in shells are reported. Yambo by default consider all the gvector determined by the energy cutoff of your ground state calculations. If you want, you can reduce them by using MaxGvecs (in this case 800), then yambo will close the shells anyway, so it will consider the closets number of your choice that close a shell (here 773). MaxGvecs it is not a convergence parameter, just say the code the number of vectors to be ordered and considered for the following calculations. If you set MaxGvecs you cannot set a variable with Gvecs > MaxGvecs in the following calculations, for this reason if you do not have space problem, it is a good choice do not define it and do the setup with the MaxGvecs coming from the ground state calculation, which is the default.
Hope it helps,
Daniele

[muthu]

dear Daniele i am sorry for previous message, i tried to manage above task. i jus convered LiF input file available in tutorial to quantum espresso format and tried to inilize yambo with MaxGvecs 10600 , 10777 , 10800 , 10900. the following is input and outputs of my run for LiF with quantum espresso input file

input-output.tar.gz

which MaxGvecs is correct ?
Few point to clarify:

1. except for 10777 in other out file one additional line is printed for example
| MaxGvecs= 10489 RL # [INI] Max number of G-vectors planned to use is printed in r-10600_setup, corresponding MaxGvecs 10600.

it is not printed in output for MaxGvecs = 10777 why?

2. for MaxGvecs 10800 and 10900( two are hihger then 10777) at section 3.0 of output files error message is appered and calculation was set to perform for gamma only automatically. why?
[03] Transferred momenta grid
=============================
[WARNING][RL indx] 2 equivalent points in the rlu grid found

[RL indx] X grid is not uniform. Gamma point only.

i request to clarify these question and is this way to optimize MaxGvecs correct?. which MaxGvecs should i choose?

[Daniele Varsano]

Dear Muthu,
let me ask you again to fill your signature with you name and affiliation. Thanks.
What do you have to care, is to have a converged ground sate with respect the plane wave cutoff of quantum espresso. Next for optics, yambo will need less Gvectors. There is not a correct MaxGvecs, yambo do the setup considering the maximum gvectors available from the qe run.
1) The value in the report is reported when different from the max available from the qe run.
2) Please note you are setting in some input more G vectors that the ones considered in the ground state, which is nonsense as you do not have the wfs component
3) Please use nscf and not band runlevel in qe.

Again, the best think to do is to not set MaxGvecs as it is not a convergence variable, and there is nothing to be optimized, it is needed only if you want to reduce your gvector inizialization in the setup. Consider that at this level yambo did not do any calculation but just prepared the database needed for the following calculations. If you do not set the MaxGvectors variable yambo will consider all the Gvectors available. In most of the case if you want to save space in your disk you can reduce it if you know that you will not need all the charge gvectors, as it is often the case.
Hope it helps,
Daniele