[Pw_forum] negative (alpha)^2*F(w)

[Ali Tavana]

Dear QE users,

I have a question about e-ph lambda, calculated by "matdyn" program. I've found that for some frequencies the quantity "(alpha)^2*F(w)/w" or "dos_a2F(w)/w" can be negative, most probably because of the negative (imaginary) frequencies (I can't believe a2F(w) become negative!). In "matdyn" program these negative values are considered in lambda calculations. Should one remove these negative values as these imaginary frequency modes can never exist in the system? then where are those phonon branches? I think negative values of frequency can show in some manner more strong electron structure interaction, so what do you suggest one should do?

regards,
Ali