Hi, Thanks for the reply. I am calculating a real system, with 32 orbitals per unit cell. Moreover, I need to use supercells so that I can simulate periodical boundary conditions. For example, I want to scatter along x direction. Also, I want z direction to be finite and y direction to be periodical. Since kwant does not allow hoppings beyond nearest unit cell in leads, I have to make a supercell that contains all unit cells in y direction! Best! Chong Wang ________________________________ From: Joseph Weston <joseph.weston08@gmail.com> Sent: Wednesday, May 11, 2016 8:24 PM To: Chong Wang Cc: kwant-discuss@kwant-project.org Subject: Re: [Kwant] scatter without a center area Hi, I want to calculate conductance between two different leads. This is what I have tried: 1. build an empty center area. This does not work because kwant doesn't know how to attach leads to an empty area. 2. use lead_1.attach_lead(lead_2). Kwant.plot does not correctly plot two leads, so I suppose it doesn't work. I don't want to build a center area that is the same with one of the leads, because my system is very large and I suppose this will be time-consuming. I'm afraid that the way Kwant works at the moment means that you will need to build a central system if you want to calculate transport properties! On some level this makes sense, as you need to define how the two leads are coupled. If this is really inhibiting your ability to actually solve problems, then the only short-term solution would be to use Kwant to calculate the modes in the leads and then set up the scattering problem manually. This would probably be exponentially more work for *you*, however. How wide are your leads that this is really a problem? Did you benchmark the runtime? Happy Kwanting, Joe