[Kwant] On-site potential only at the edge of the sample in Kwant

Dear developers, I’m interested in investigating the influence of the edge potential of the sample. For example, in an example by tutorial “quantum_wire.py”, I would like to put on-site potential only at the edge atoms. One could determine whether the site is edge or not by reading the number of neighbors of the site by using “degree”. For example, if the degree is 3 there is an on-site potentials , else 0. Is there any example code from which I can learn to use this function? Best, Dongwook.