Negative elements in electron-phonon coupling matrix

[Patrick_1396]

Hi,

I am trying to calculate deformation potentials for use in scattering rates for cubic silicon carbide and cubic boron nitride. To do this I am calculating the electron phonon coupling matrix following the method given here https://journals.aps.org/prb/abstract/1 ... .104.19520

However, as SiC and cBN are polar, I am calculating the total and long range elements and subtracting the long range elements. This results in negative values in the elph coupling matrix.

The figures attached show the electron phonon coupling elements along directions of interest. In cBN_aco.png, these are short steps away from the conduction band minimum of length 0.01 2pi/a in the direction given on the x-axis. In cBN_opt.png, these are paths from the conduction band minimum at [001] to a perpendicular conduction band minimum at [100] (f scattering).

I am unsure of how to proceed with this. Do the negative values have meaning or is it some mistake in the input files?

Thanks,
Patrick.