Thanks a lot. I tried to install the cons_laws_combined, but I get the following error message:
"LINK: fatal error LNK1181: cannot open input file 'lapack.lib'" Is there some package or installation I am missing? Best regards, Camilla -----Original Message----- From: anton.akhme...@gmail.com [mailto:anton.akhme...@gmail.com] On Behalf Of Anton Akhmerov Sent: 8. januar 2017 16:35 To: Tómas Örn Rosdahl <torosd...@gmail.com> Cc: Camilla Espedal <camilla.espe...@ntnu.no>; kwant-discuss@kwant-project.org Subject: Re: [Kwant] Regarding smatrix and spin Hi Camilla, everyone, I've slightly modified Tómas's example to a case where the spins do get coupled, check it out: http://nbviewer.jupyter.org/url/antonakhmerov.org/misc/spin_conductance.ipynb I've also provided more detailed installation instructions in the notebook. Cheers, Anton On Sun, Jan 8, 2017 at 2:45 PM, Tómas Örn Rosdahl <torosd...@gmail.com> wrote: > Dear Camilla, > > For a Hamiltonian with degeneracies due to a conservation law, the > scattering states will in general not have a definite value of the > conservation law. In your case, Kwant returns scattering states that > are arbitrary linear combinations of spin up and down, so it is not > possible to label the amplitudes in the scattering matrix by spin. > > However, in Kwant 1.3 a feature will be added that allows for the > construction of scattering states with definite values of a > conservation law. See here for an explanation of the basic idea behind the > algorithm. > > We're currently working on implementing this feature in Kwant itself. > The good news is that we're practically done - here is a link to a git > repo with a functioning implementation. After you clone the repo, > check out the branch cons_laws_combined, which contains a version of > Kwant with conservation laws implemented. This notebook contains a > simple example to illustrate how to work with conservation laws and the > scattering matrix. > > I invite you and anyone else who is interested to give it a try. We'd > appreciate any feedback! > > In your case specifically, there would be two projectors in the new > implementation - P0 which projects out the spin up block, and P1 that > projects out the spin down block. If they are specified in this order, > then the spin up and down blocks in the Hamiltonian have block indices > 0 and 1, respectively. In the new implementation, it is possible to > ask for subblocks of the scattering matrix relating not only any two > leads, but also any two conservation law blocks in any leads. To get > the reflection amplitude of an incident spin up electron from lead 0 > into an outgoing spin down electron in lead 0, you could simply do > smat.submatrix((0, 1), (0, 0)). Here, the arguments are tuples of indices > (lead index, block index). > > Best regards, > Tómas > > On Fri, Jan 6, 2017 at 3:46 PM, Camilla Espedal > <camilla.espe...@ntnu.no> > wrote: >> >> Hi again, >> >> >> >> This question is basically the same as this: >> https://www.mail-archive.com/kwant-discuss@kwant-project.org/msg00076 >> .html >> >> >> >> I want to calculate some things using the scattering matrix. I >> started out with a very simple system, most basic two-terminal >> system. For some energy there is one propagating mode. I now add >> matrix structure to the mix (just multiply by s_0 everywhere) and >> there are now 2 propagating modes (which makes sense). >> >> >> >> Now, if I look at the reflection coefficients for lead 0 by using >> submatrix(0,0), it is now a 2x2 matrix after I introduced the >> matrices. How are the elements ordered? Is it >> >> >> >> [[r_upup, r_updown],[r_downup, r_downdown]] >> >> >> >> I know that I could make two lattices, but since I do not plan to use >> the other functions such as transmission. I just want the smatrix. >> >> >> >> Hope you can help me, and thanks in advance. >> >> >> >> Best regards, >> >> Camilla > >
