[Kwant] lead self energy

Dear kwant community, I am new in Transport and kwant. I have two simple questions regarding the lead, I appreciate any reply. 1-The lead's self energy is in principle a complex number. In kwant, If I want to add the self energy of a lead by hand, I can add the real part of it to the on-site energy of the site that lead is connected to. Where should I add the imaginary part of the self energy? 2- If I know the value of the level width function (\Gamma = 2πρt^2 = 1), and the lead is a 1D chain, can I calculate the value of the coupling parameter, t? Is there a way to obtain the DOS of the lead and then get t? Bests Chung