Generalize implementation to treat non-Hermitian models#106
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- also a fix for an error in the docs CI (add a docstring for `TightBindingTerm`)
…k` for multiple/single **k**-points - `spectrum_single_k` now handles case where a *single* **k**-point is provided and `spectrum` is strictly for *multiple* of **k**-points - by splitting up like this, we also enable the introduction of convenience method for 1D models, using `spectrum(..., ks)` with a plain (abstract) vector of real numbers; this is just much nicer in day-to-day use.
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Seems to work well now; there's some examples in the preview docs. A few things that would still be good to do before merging:
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- mainly, this is a matter of lifting 1D properties (points and unit cell boundaries) to 2D points - while there, we also fix a few old bugs (e.g., the fact that `context.limits` was not properly propagated, which made visualization of model terms with different extents display in a way where their overall extent was not comparable) - co-developed with Claude
- also fix some writing that referenced terms hopping the opposite way relative to what they actually did - extend non-Hermitian SSH example a bit
…ired" - This ensures that every term in a nonhermitian TB model has a counterpart that it would be mapped to under Hermitian conjugation. This is just much more natural and aligned with what a user would expect. The issue only arose for diagonal blocks of a Hamiltonian, with the canonical case being e.g., a (2c|A) EBR model in p4. - This also fixes a related issue, arguably a bug, in the (ANTI)HERMITIAN case, where some orbits weren't sufficiently "wide" (not enough hopping terms) to close under (anti-)Hermiticity, unless `Rs` was provided in such a way that for every positive element `R` there was also a negative element `-R`. We fix this by explicitly checking in `add_reversed_hoppings!` whether for every a→b+R term of separation δ, there is a corresponding b→a-R term at separation -δ.
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I will merge this as-is now Antonio: I've tested the new functionality in a number of ways and I'm confident it's sound. There are also a few fixes and improvements that aren't related to the non-Hermitian aspect: but they're all in their own separate commits. So I'll merge without squashing. |
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This allows us to build non-Hermitian tight-binding models via
tb_hamiltonian(cbr, Rs, Val(NONHERMITIAN)).There's some restructuring of the various structs here to encode the kind of hermiticity a model has in the type domain, so that we can be guaranteed that
spectrumtype-stably returnsFloat64in the Hermitian case. Aside from that, it's actually mainly a matter of removing assumptions about hermiticity.Pushing early (WIP; docs e.g., are not yet done), to see what docs and CI look like.