Dear Sir, I want to assign a particular sequence of site values on a particular line (a number of lines) of a zigzag graphene nanoribbon. For example, the bottom zigzag line. let's say, from the left to right there are 10 sites and I want to put the onsite values as [1,2,3,...]. I was able to get the information about the sites that are in the bottom line and have assigned the site values accordingly. But the problem is that each time I finalize the system, I get different onsite values along the bottom line. Is there any way to resolve this? Or maybe this approach is not the right way to do that. A part of my code is given below ======================== def make_system(W, L, no_of_line): ## scattering region ## sys = kwant.Builder() sys[lat.shape(cross(W,L), (0,0))] = 0 sys[lat.neighbors(1)] = -1. #######INFO of the line######### line=[] for site in sys.expand(lat.shape(cross(W,L), (0, 0))): #print (site.pos[0],site.pos[1]) line.append(site.pos[1]) line=set(line) line=list(line) line=sort(line) i=1 for site in sys.expand(lat.shape(cross(W,L), (0, 0))): for j in range(0,no_of_line+1,2): line_no=j if (site.pos[1]==line[line_no] or site.pos[1]==line[line_no+1]): sys[site]=i i=i+1 ######################## With Regards, Sudin