Yambo Community Forum

Dear all,

Is YAMBO currently possible to calculate two-photon absorption (TPA) spectra?

I have seen several papers that have calculated TPA using Yambo (https://doi.org/10.1103/PhysRevB.98.165126, https://doi.org/10.1103/PhysRevB.96.245109). There is also a post-processing script (https://github.com/yambo-code/yambo-min ... tion_PP.py) that "extract two-photon absorption and intensity-dependent refractive index from ypp". So yambo is possible to calculate TPA?

If possible, how to set the parameters in the input file? I couldn't find any tutorials for calculating TPA in yambo or lumen. According to this NLAbsorption_PP.py, at least two field intensities are needed. But I don't know how to set. Also, since TPA is a third-order process, why does the NLAbsorption_PP.py script require input files of the first order("_order_1") instead of the third order?

Bests
Zhengran

Dear Zhengran

sorry for the late reply.

Yes in principle it is possible to extract TPA with Yambo, even if it is rather complicated.

The procedure is described in
https://journals.aps.org/prb/abstract/1 ... .98.165126
in section III.A

In practise you choose and energy range you are interested in, for example between 1 and 2 ev,
than a number of frequencies you want in this range, for example 40 points.

Then you run a simulation with a sinusoidal field at a given intensity E, you repeat the calculation with intensity E/2 and E/4.

You subtract the different polarization using the formula Eq. 18 of https://journals.aps.org/prb/pdf/10.110 ... .98.165126
and the Fourier transform the result.

I will try to prepare a tutorial on this kind of calculations

best
Claudio

Dear Claudio,

Thanks for your instruction! Now I generally understand the calculation procedure. I will try to extract the polarizations and do the Fourier transform. But I'm afraid it is not easy for a newbie like me.

It would be so great to see a tutorial on this.

Best,
Zhengran

Dear Claudio,

I figured out how to calculate TPA. Thank you very much for the previous tips.

I have one more related question: how to consider the effect of different polarizations of the E field on TPA? Since the calculation uses the intensity dependent first order susceptibility, I have no idea which tensor elements are non-zero. (I only know the non-zero elements of second/third order susceptibility)

Best,
Zhengran

Dear Zhengran

setting the polarization in input you can select the three components,
but I understand that if you want off-diagonal terms you need two fields.
We are adding a second external field to yambo, and we will release a new version soon.

best
Claudio