Dear Adel, Thank you very much for your kind help.I want to use kwant to calculate the transmission for bulk system because of the paper Phys. Rev. B 86, 115455. However, ky for the lead and the scattering region is not very clear in Kwant when we use kwant.wraparound. When we use smatrix = kwant.smatrix(sys, energy, [ky]) to calculate the transmission of the bulk system,we do not know if the ky here can affect the scattering region or not. I have tried a system with more args, for example smatrix = kwant.smatrix(sys, energy, [VG1,VG2,ky]), (Here ky must be put as the third one), the definition of the onsite potential should be given as “def onsitepotential(site,VG1,VG2)”. I do not know if it is a bug or I just do not find the right way to use the kwant.wraparound. I think the developers may know the reason. Best, Khani Hosein