Dear Amrita, Yes, you can add the two builders as follows: left_lead1+=left_lead2
but in the new version of kwant, the operator += for builders is deprecated. So, you better use: left_lead1.update(left_lead2) and then you add your missing hopping, before you attach the lead: left_lead1[(lat(0,0),lat(0,-1))]=t I don't know why you separate your lead into two parts and then build it again, but you can get it directly in one shot. I hope this helps. Adel On Fri, Feb 23, 2018 at 10:04 PM, amrita chapagain < amritachapag...@gmail.com> wrote: > Thank you Adel for prompt reply. I have another query here. Can I add > these two system together incorporating missing hopping elements? > -- Abbout Adel