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pablosanjose / Elsa.jl

Efficient lattice simulation algorithms - a Julia library
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Create LazyHamiltonian (with fields) #45

Open pablosanjose opened 4 years ago

pablosanjose commented 4 years ago

Following #44, we should also refactor lazy Hamiltonians (defined on a non-materialized superlattice), so that it can contain fields, that have no reason to be part of a conventional Hamiltonian (since all fields are materialized already in the relevant matrices).

The unitcell(::Hamiltonian,...) codepath, that currently builds first a superlattice and then expands the Hamiltonian on it, could now create an intermediate sham::LazyHamiltonian = supercell(h,...) containing the fields passed to unitcell, that then gets materialized by unitcell(sham) as a conventional Hamiltonian, applying the fields on the way.

That way we also reduce the current overlap between hamiltonian.fields and the possibility of creating a ParametricHamiltonian, which can be seen to fulfill similar goals. We should keep ParametricHamiltonian as a way to apply a model in place to any sites, and the fields mechanism as a way to transform existing hoppings and onsites, when growing a system or using it lazily.

pablosanjose commented 4 years ago

This will need to be revisited in view of the new onsite! and hopping! modifier concepts that were introduced with ParametricHamiltonian and that replace fields.

In any case, I see little urgency in this functionality at the moment, so priority is low unless a compelling use case is brought forward.