Reasonable values of degaussw

[tswang]

Hi all,

I am working on the thermal conductivity from the EPI for doped materials like the example of B-doped diamond.

I would like to know the reasonable minimum degaussw. That's because I probably need a very small value since the doping move the Fermi level below VBM by only 3-100 meV. On the other hand, the value cannot be too small because of the native phonon effect. For scf and nscf, I use 1 mRay degauss. Please also comment on this value.

I look forward to your comments. Thank you very much!

Tianshi Wang
Ph.D. candidate, MSEG
University of Delaware, DE USA

[roxana]

Hi,

You will need to run convergence tests for various smearing values as well as k- and q- fine meshes. In principle you can use a smearing value as small as 1 meV but you will need very dense meshes. I would say a values of 10 meV is good in most cases, but even in this case you will need to check convergence with respect to the k- and q-meshes.

Best,
Roxana

[tswang]

Dear Dr. Margine,

Thank you very much for your prompt reply.

So a smearing (degaussw) less than 1 meV is usually not needed. The degaussw and k-mesh size are correlated during the convergence test. Therefore, is it ok that I set degaussw as 1 meV and only test the size of k and q meshes?

Do you have any experiences on how large the mesh should be? I am using a k-mesh of 100x100x100 and q-mesh 35x35x35 which doesn't seems very well.

Thank you again for your help.

Tianshi Wang

[roxana]

Hi Tianshi,

Unfortunately, without testing there is no way to know if a value is converged or not. You can do smaller meshes a see how the value of interest changes.

Best,
Roxana