Matsubara function?

[jydai]

Dear All,

I am asking here that if the finite temperature Green function, .ie., Matsubara Function, is involved in Yambo? If it is, what's the keyword to control it?

Best wishes,

Jiayu Dai
--------------------------
Dept. Phys.
NUDT

[Davide Sangalli]

Dear Jiayu Dai,
the yambo code is based on the T=0 many-body perturbation theory.
Thus Matsubara Functions are not computed.

The electronic temperature which you can set in input should be regarded only as a smearing parameter for your calculations.


However (if I'm not wrong, please verify!) in case a retarded quantity is computed using a static self-energy / kernel, this corresponds in practice to the analytic continuation of the Matsubara Green function on the real-time axis and the temperature dependence is physical. This holds for QP corrections computed at the HF/COHSEX level or for the BSE where the kernel is usually static (yambo should switch automatically to the use of retarded Green's functions at finite temperature). It does not hold instead, for example, for QP corrections computed at the GW level since the GW Self-energy is frequency dependent.

D.

[jydai]

Dear Davide,

Thanks for your reply. I think you are correct as my understanding here, because the Matsubara frequency should be included here.

So, if i want to add this part (Matsubara fucntions) in Yambo, could you give me some advice where should i begin, and which part should i change?

Best wishes,

Jiayu
----------------------
Jiayu Dai
Dept. Phys.
NUDT
https://www.researchgate.net/profile/Jiayu_Dai

[Davide Sangalli]

If you are just fine with a static self, energy, then you can ask yambo to gives in output the G^{r}(\omega) green function.

If you want to compute the GW Matsubara Green function you should add extra terms to the GW Self-Energy.
There is this article of which I'm aware: PRB 74, 033101 (2015). The retarded self-energy is quite involved

In yambo the folders to look for are src/qp and src/qp_control
In particular QP_ppa_cohsex is the subroutine computing the GW self energy (within the plasmon-pole approximation) or QP_real_axis (without ppa)
We are probably going to re-organize this part of the code to make it more modular.

D.

[jydai]

Thanks Davide. Hope your new version released.

I will read the paper, and find what can i do now.

Best.

Jiayu
--------------------
Dept. Phys.
NUDT
ampg.nudt.edu.cn