Hello, I'm trying to study a chain of molecules, say A-B-C-D, each with a unique onsite energy and hopping parameter associated to the adjacent site. Electrodes are connected in the conventional way ...-x-x-x-A-B-C-D-x-x-x....
I would like to produce an I-V curve using Landauer Formula from -1V to +1V. I would think that for negative bias, it would be correct to compute transmission probability from lead 1 to lead 0 (i.e. smatrix.transmission(0,1)) as opposed to lead 0 to lead 1 for the positive bias case. Doing so does not result in any difference in the transmission probability. However, if I reverse the sequence, I do get a different transmission spectrum. 
Shouldn't a reversed sequence result in the same transmission probability as in switching the direction of measurement lead1 to lead0?