how to output the screened Coulomb interaction W

Dear Sir,

I want to know how to output the screened Coulomb interaction W. Is it using the label plot_coul? If yes, how to further process to get the μ?  
ps: μ is a double Fermi-surface average of the screened Coulomb interaction: μ=Nf<<<k, -k|W|k', -k'>>>.

Thank you so much.

Sincerely,

zpy