Dear Andreas, I investigated your code and everything seems correct. I checked your claim, and found it true! For large value kapp=0.0001, the S matrix is unitary. The same for Kappa=0 or kappa <1E-13. Around Kappa=1E-9, it is not unitary (at least not unitary with the precision set in kwant) I am still puzzled and did not find an answer for that. The only remark I can make is that the edge state at this energy is degenerate and I remember, a case with kwant having a problem happening at the degenerate states.
If it happens that you find the answer, I will be interested to read it. Best regards, Adel On Thu, Dec 10, 2020 at 5:49 PM Andreas Bereczuk <[email protected]> wrote: > Dear all, > > i used a slightly modified "discretize.py" code of > https://kwant-project.org/doc/1/tutorial/discretize (see attached file) > > and added the term > > """ + kappa * kron(sigma_z,sigma_0) """ > > to the hamiltonian (splitting up the different spins). When checking the > unitarity of the scattering matrix at energy=0 by applying the function > "check_unitarity(matrix)" for > > kappa=0 and kappa=10**(-9) the unitarity-error is increasing from order > 10**(-13) to 10**(-6) ! > > Why is the error of $ S^\dagger S$ getting so high? > > > Thanks in advance! > > Andreas Bereczuk > > -- Abbout Adel
