Dear all, I am trying new Kwant 1.3 features on a very simple example of graphene monolayer, and, apart from a standard well-working code I add: for x in sys.sites(): x.family.norbs=1 for x in leadxp.sites(): x.family.norbs=1 for x in leadxm.sites(): x.family.norbs=1 (to avoid norbs not defined error) ... J_0 = kwant.operator.Current(sys) wf = kwant.solvers.default.wave_function(sys, energy=0.01, args=[phi,chempot,0]) psi=wf(1) current = J_0(psi) I get the following suspicious message: The size of the file /home/sergey/.local/lib/python3.6/site-packages/kwant/operator.cpython-36m-x86_64-linux-gnu.so is 2734 KB. Do you really want to load it? After answering yes, I get the error message, caused by current = J_0(psi) : "The debugged program raised the exception unhandled ValueError "vector is incorrect shape" File: /home/sergey/.local/lib/python3.6/site-packages/kwant/operator.cpython-36m-x86_64-linux-gnu.so, Line: 529 Break here?" Could anyone guess, what goes wrong? N.B. I have installed Kwant with a command pip3 install kwant Thanks, Sergey