Dear all, Facing a problem to fix lead in a desired direction. In fact, I can't understand how to count the sites and this make trouble. For better, let me refer to to the documentary paper on "Kwant: ---- transport" of C.W.Groth et.al. in example of appendix D4. 1. sys[lat.shape(ring,(10,0))] = 0; > whether the origin (0,0) or the site coordinate specified by (10,0) is to be taken as origin for fixing the location/position of the leads? How then the desired choice of to fix lead position is to be made ? 2. sym=kwant.TranslationalSymmetry((-2,1)); > I am sorry I cannot follow meaning of the symmetry direction vector! I cannot match the idea with the kwant construction of the lead in the direction of (-2,1) 3. lead[lat((x,0) for x in range(-6,6))]=0; > I understand total 13 sites counted from (-6,0) to (6,0); Where I am wrong in understanding ? 4. sys.attach_lead(lead,lat(0,0)); > Is it not possible to use the code "lead.(reversed)" ? Though every question is answered in the paper still my ignorance blockheads my real conception. Unless I have clear conception I cannot use my Kwant, an extremely powerful weapon, flexibly to design my nanosystems. I am waiting for your nice and exemplary advice and instruction from the forum. All regards. K.K.Ghosh