Dear Pablo, Yes, now, everything works. Thanks a lot for Your help. Best Regards, Pawel

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07/31/20 10:13 PM >>> Hi again Paweł,

I realized that `substutited` *returns* a new builder, and does not change it in-place. The docs of `magnetic_gauge` were misleading there. You can simply replace ``` l_lead = l_lead.substituted(peierls='peierls_llead') ... r_lead = r_lead.substituted(peierls='peierls_llead') ``` in your code, and should work.