Should the fine k-mesh and the fine q-mesh be commensurate?

[AgentZero]

Dear all,

As mentioned in the title, is fine k-mesh 30x30x30 with fine q-mesh 20x20x20 reasonable or not?

Best regards,
Miao Gao

[sponce]

Dear Miao Gao,

In general, no they do not have to.
Notable exceptions: superconductivity (Eliashberg stuff) and iterative Boltzmann transport equation (mobility). The last one is not yet release (will be in March).

Best,
Samuel

[AgentZero]

Dear Samuel,

Thank you very much for your reply! In my understanding, if we only calculate the e-ph constant lambda, and
determine the superconducting Tc by Allen-Dynes formula, these two fine meshes could be uncommensurate. Am I right?

Best regards,
Miao Gao

[Nandan]

Hi,

I had a related question. For GaAs I have used two fine q-mesh grids: 1. 50x50x50 and 2. 80x80x80
keeping the fine k-grid the same (a path along L-G-X with 25000 points). But I get two different
results for Im(Sigma) as shown in the link below. They look similar but the magnitudes differ significantly.

http://www.mediafire.com/?f22v94bes7rwa

All other details of the calculation are identical including the machine on which the job was run.

Any idea why this is happening?

Thanks and regards,

Nandan.