Yambo Community Forum

Posted: **Fri Oct 01, 2021 3:52 pm**

Dear Developers,

I am trying to study how the exciton strength evolves as a function of q.
I have 51 points in the irreducible Brillouin Zone. So, I=in order to do so, I performed a BSE computation from q=1 to q=51.

Then I sorted them according to their energy in order to distinguish bright and dark excitons.
Let's focus on the evolution of the first bright exciton. I know that its strength is normalized to the Maximum Residual Value so that it is listed as having strength 1.0

However what is strange is the following thing:

# q Maximum Residual Value
1 .69351E+00
2 .15871E+06
3 .63177E+06
....
51 .75359E+08

It seems really strange that it keeps increasing and, most strange of all, that it increases of six orders of magnitudes passing from q = 1 to q = 2

Am I doing something wrong or am I interpreting this number wrong?

Best,

Davide Romanin
-----------------------------------------------------
Post-doctoral fellow
Institut des NanoSciences de Paris
Sorbonne Université, CNRS
4 place Jussieu,
75252 PARIS Cedex 05

Posted: **Fri Oct 01, 2021 4:01 pm**

Dear Davide,

which version of the code are you using?
There was a bug in the definition of the finite-q residuals as it as defined considering the q->0 limit also for finite q:

./ypp/excitons/excitons_sort_and_report.F

Code: Select all

127    Residuals(:) = Residuals(:)*real(spin_occ,SP)/(2._SP*pi)**3*d3k_factor*4._SP*pi/q0_def_norm**2*HA2EV

which has been corrected in the latest release as:

Code: Select all

128    if(iq==1) q_norm=q0_def_norm**2
129    if(iq> 1) q_norm=iku_v_norm(BSqpts(:,iq))**2
130    Residuals(:) = Residuals(:)*real(spin_occ,SP)/(2._SP*pi)**3*d3k_factor*4._SP*pi/q_norm*HA2EV

can you check if you are using a release still containing the bug?

Best,
Daniele

Posted: **Fri Oct 01, 2021 4:05 pm**

Dear Daniele,

Yes I have the 5.0.2 version

I checked and indeed the line is the one with the bug.

Should I just modify it with the new three lines you wrote?

Davide

Posted: **Fri Oct 01, 2021 4:18 pm**

Dear Davide,

yes, these are the lines, but you need to define and import from modules the desired quantities.
In general, I suggest you update to the last release, as other small bug have been fixed.

Otherwise find the patch in attachment,

Best,

Daniele

Posted: **Fri Oct 01, 2021 4:39 pm**

Dear Daniele,

Ok thanks a lot!

Yes I will update to the new version, but it was just to do a rapid check

Best,

Davide

Yambo Community Forum

Strange behavior of exciton maximum residuals

Strange behavior of exciton maximum residuals

Re: Strange behavior of exciton maximum residuals

Re: Strange behavior of exciton maximum residuals

Re: Strange behavior of exciton maximum residuals

Re: Strange behavior of exciton maximum residuals