Weight of excitation

[xtbu]

Dear developers,
I am wondering about the wieght in ypp output inducing from ypp -e a as:

Code: Select all

#    Band_V       Band_C       K  ibz       Symm.        Weight       Energy
#    
     32.0000      33.0000     12.0000       6.0000       0.1080       1.4859
     32.0000      33.0000     12.0000       5.0000       0.1080       1.4859
     32.0000      33.0000     12.0000       4.0000       0.1080       1.4859
     31.00        34.00        12.0        6.000       0.6421E-1     1.506   
     31.00        34.00        12.0        5.000       0.6419E-1     1.506   
     31.00        34.00        12.0        4.000       0.6419E-1     1.506

If I want to konw the contributions of the trasition, like 32-33 as above, I need to count the contribution 0.108x3 or just 0.108?
An other thing is the total weight are not equal 1, far less than 1. Why?

Thanks!

xt Bu

[Davide Sangalli]

Dear Xiangtian Bu,
you should count 0.108x3

The total weight is not 1 because, in the output are reported only the weights of the most relevant transitions.
There is a default threshold at 5% of the total weight. You can lower the threshold via the variable "Weight_treshold"

Best,
D.

[Daniele Varsano]

Dear Xiangtian Bu,

the variable controlling the threshold of the transition printed in the output is "MinWeight" that will be substituted with "Weight_treshold" in the next release.
Best,
Daniele

[claudio]

Dear Xiangtian Bu,

probably the name Weight is not so correct, it should be better to call it "percentage contribution" to the exciton

best
Claudio

[xtbu]

Thanks, Davide, Daniele and Claudio,
So is the weight stands for |A_eh|^2？Where the A is the prefactor of |S>?
Thanks!

Xiangtian

[Daniele Varsano]

Dear Xiangtian,

yes, the weight is defined as you indicated.

Best,
Daniele

[xtbu]

Dear all,
I got the exciton dipoles as described here"http://www.yambo-code.org/wiki/index.ph ... e_excitons".
And it is |A_eh<e|D|h>|, and whose square is proportional to oscillator strength. And I obtained the dipoles through Residuals as decroced here as :
Res=8pi/(q^2\Omega Nq)*|BS_R|^2. But why the two method has a different value of dipoles? I think |A_eh<e|D|h>|^2 should be equal as |BS_R|^2 here.

Thanks!

Xiang tiang

[Daniele Varsano]

Dear Xiang,

I'm not sure I've understood your question,

I think |A_eh<e|D|h>|^2 should be equal as |BS_R|^2 here.

This is correct, these are the weighted transition dipoles, and the residuals are defined as you say, by multiplying them by a prefactor.
Maybe can be useful to look at this thread.

Best,
Daniele

[pyadav]

Dear team Yambo,

How can I get a rough estimate of the size/radius of the lowest energy exciton in any material after BSE calculation.

Thank you,
Pushpendra

[Daniele Varsano]

Dear Pushpendra,

you can have an estimation by plotting the corresponding exictonic wave function, e.g. in 1D where the two other dimensions are averaged and then fit the envelope function with a hydrogenic wave function in the case it applies.

Best,
Daniele