Thanks for your reply. In the kwant paper, I think fig 7 indicates ~1000GB memory is needed for such a system. Also, I only replicated my unit cell twice in the y direction. It seems that I need to figure out some tricks to work around this. Chong ________________________________ From: Joseph Weston <joseph.weston08@gmail.com> Sent: Wednesday, May 11, 2016 9:53 PM To: Chong Wang Cc: kwant-discuss@kwant-project.org Subject: Re: [Kwant] scatter without a center area Hi, `lead.cell_hamiltonian()` gives 32000. The thickness of my slab is 50. Is this something not possible to calculate? Ok, now it certainly makes sense that the memory blows up; the kwant paper[1] indicates that the memory requirement for solving this sort of size should be ~ 100GB. Anton reminded me of a workaround written by Christoph for dealing with periodic systems. You can find the code over here[2] (if you don't want to download it using git you can get the raw python module here[3]). You should be able to use this instead of replicating your unit cell in the y direction, which should drastically reduce your memory/runtime requirements. Thanks, Joe [1]: http://downloads.kwant-project.org/doc/kwant-paper.pdf Kwant: a software package for quantum transport<http://downloads.kwant-project.org/doc/kwant-paper.pdf> downloads.kwant-project.org Kwant: a software package for quantum transport Christoph W. Groth,1 Michael Wimmer,2 Anton R. Akhmerov,2,3 and Xavier Waintal1 1CEA-INAC/UJF Grenoble 1, SPSMS UMR-E ... [2]: https://gitlab.kwant-project.org/cwg/wraparound [3]: https://gitlab.kwant-project.org/cwg/wraparound/raw/master/wraparound.py