Re: [Kwant] Symmetry and leads

[christoph . groth]

Joseph Weston wrote:

- A more general solution is to do what Anton proposed. I include a sample script below.

sym.add_site_family(lat.sublattices[0], other_vectors=[(-1, 2)]) sym.add_site_family(lat.sublattices[1], other_vectors=[(-1, 2)])

Thanks for this. I had tried do do the following:

        sym.add_site_family(lat, other_vectors=[(-1, 2)])

instead of calling `add_site_family` for each sub-lattice, and it did not work. I therefore thought that my understanding was flawed, but it seems that for a polyatomic lattice one has to manually add each sub-lattice. Maybe a word in the documentation would be useful to prevent this potential pitfall

for sl in lat.sublattices:
   sym.add_site_family(sl, other_vectors=[(-1, 2)])

Christoph

Thanks for brining up this issue, this is certainly one aspect of Kwant that could (and will) be improved in the future. Even though add_site_family is part of the public API, it is something of a second-class citizen. It was not meant to be used commonly. Only after publishing Kwant 1.0 we realized that add_site_family can be actually useful for choosing the orientation of lead unit cells. In fact, “add_site_family” should be have been named “add_lattice”, as it does not work for general site families but only for instances of kwant.lattice.Monatomic. It could also accept kwant.lattice.Polyatomic instances as you suggest. Fixing all this in a backwards-compatible way would be messy and confusing. I’ve made a note about this issue for the next major version of Kwant. For now, I recommend using what has been suggested above, i.e.:

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