Convergence of lambda and Tc

[eliephys78]

Dear All,

I have been testing the convergence of lambda and Tc for Al as an exercice changing the kf grid for a fixed qf grid: I chose:

nk1=6
nk2=6
nk3 =6

nq1=12
nq2=12
nq3=12

nqf1=15
nqf2=15
nqf3=15

with changing nkf grids as 30x30x30, 40x40x40 and 50x50x50 but i still didnt get convergence (for different degaussq). Results are fluctuating. Can anyone tell me what could the possible problem be? Havent I reached convergence for the nkf and nqf grids)?

I can show you the results on a graph but I do not think I can post images from my computer into the forum. Any other way?

Thanks

[sponce]

Dear eliephys78,

The convergence is indeed very slow.

In the case of MgB2, I used 60x60x60 but did not reach full convergence (there are still some small fluctuations).

You can look at Fig 8 from PRB 87, 024505 (2013) for a convergence of MgB2. As you can see there are still some changes.

Best,
Samuel

[eliephys78]

Dear Samuel,

Thank you for your reply. One more question:

Regarding the convergence , does it have to be with respect to degaussw and fsthick? or just by degaussw? How to determine the value of fsthick for each system?

regards

[sponce]

Dear eliephys78,

You should increase fsthick until your physical properties do not change anymore.

If you do not want to converge it, you can just put a large value.

Best,
Samuel

[eliephys78]

Thanks for your reply.

Sorry but I have a probably trivial question: I have read somewhere on the QE forum that \lambda (the electron phonon coupling) only exists for metals and it can only be calcuated for metals for QE. Then how are we able to calculate it in EPW fpr graphene and other semiconductors or types of materials?

Regards

[sponce]

Hello,

\lambda is not the electron-phonon coupling. It is the electron-phonon coupling strength (see Eq. 11 from the EPW paper).

The electron-phonon coupling is "g" (see Eq. 1 from EPW paper) and is well defined for semiconductors, insulators and metals.

Best,
Samuel