Hi Chung,

Is there a way to implement indirect hopping in Kwant? I have a cubic system and I want to add to the term describing the direct hopping between site i and j, an indirect hopping term via an intermediate site k, for all the sites in my system.

Kwant does not have a concept for "indirect" hoppings; you will have to implement something yourself, adding two hoppings to the system. You can use similar logic to the existing HoppingKind object; just iterate over all sites "i" of the system, check for the existence of sites "j" and "k" in the system. If they both exist, add the 2 hoppings, if either does not exist, do not add the hoppings. Somthing like the following should work:     lat = kwant.lattice.cubic()     syst = …     delta_j = …  # tag offset  i → j     delta_k = …  # tag offset j → k     sites = set(syst.sites())     def second_hops():         for i in sites:             j = lat(i.tag + delta_j)             k = lat(j.tag + delta_k)             if j in sites and k in sites:                 yield (i, j, k)    for i, j, k in second_hops():        syst[i, j] = hop1        syst[j, k] = hop2 Happy Kwanting, Joe