EPW Forum

Dear experts,

If the valence/conduction band edges of a material are flat in certain directions, will methods implemented in EPW, particularly for mobility calculation, still be applicable?

Thanks,
Muhammad Aminul Haque

Dear all,

I'd really appreciate it if someone could share your thoughts on it.

Mainly, I am concerned about the effective mass if a valence or conduction band becomes almost flat in specific directions. I have not been able to reach any conclusion going through the paper (https://doi.org/10.1103/PhysRevResearch.3.043022) by Prof. Ponce and coworkers.

Looking forward to your insights.

Thanks,
Muhammad Aminul Haque

Hi Muhammad,

There should not be any issue with the calculation of mobility in materials with extremely high effective mass/flat-bands. Transport code implemented in EPW uses the ab-initio bandstructure (DFT or GW(if provided as .eig file) for energy eigenvalues. There is no point where "effective mass" is explicitly calculated.

Best regards,
Sabya.

Hello Muhammad,

The code will work and produce results.

However if the band is too flat, the BTE theory is indeed not expected to hold.
In that case you will likely create polaron etc.

I would therefore be very cautious with very flat band materials.

Best wishes,
Samuel

Dear Dr. Ponce and Dr. Tiwari,

Thank you so much for you insights. I was worried whether the code will break or produce anything wild if 'effective mass' was calculated explicitly.

The limitations of BTE itself have to be taken into consideration of course, as you mentioned.

Regards,
Muhammad Aminul Haque