electronic-structure

To get this codebase up to standard, we need to add type hints. At the very least, perhaps we should start insisting that all new code has type hints added, but moreover we need to add typing to the code that currently exists.

This is a pretty large project, but luckily it can be done incrementally - I believe at this point it's a stretch goal for v1, if anyone wants to help it would be much ap

As it says, move away from keeping n_bands fixed during the SCF.

Is your feature request related to a problem? Please describe.

The SpinDensityEstimator currently does not support open boundary conditions. Once supported we can deprecate or remove the DensityEstimator since the SpinDensityEstimator has a superset of the DensityEstimator functionality.

Describe the solution you'd like

Implement open boundary conditions

Additional context

RDMs returned from pyscf are spin summed. Use https://sunqm.github.io/pyscf/_modules/pyscf/fci/direct_spin1.html#FCISolver.make_rdm12s

to return non-spin summed versions. Recombine spin-separated RDMs like run_psi4 to get spin-orbital rdms before returning to OpenFermion.

It would be good to toggle on or off real vs complex arithmetic.

Right now we (for the most part) treat everything as complex-valued, because the goal at the time was to allow for real-time electronic dynamics. For most users this is just additional computational overhead, so it would be good to implement the ability to switch between real and complex, and include safeguards to force complex if