Active space extension

[mrossinek]

Description

I would like to extend this schema to support active space-based embedding techniques.
For this to work efficiently, we need to add two additions to the schema:

1. sending MO data directly rather than AO data, in order to allow the minimal set of information to be transferred (i.e. only the active MOs instead of the full AO set)
2. add fields for the 2-body terms (electron repulsion integrals; short: eri). This will enable this schema to be used to interface two codes where e.g. one of them does not support eri-computation on-the-fly.

Questions

• How can we generalize the basis in which a matrix is provided in? I naively added some _mo_ named keywords but I don't think this scales well for the future.
• Can we encode symmetry information for the eri terms? This would permit not having to send O(N^4) numbers when up to 8-fold symmetry could be exploited.

Status

• Open for discussion

[mrossinek]

When using this for active spaces, we should also add a field in the properties schema, which can indicate the energy contribution of the inactive space. I'm open to naming suggestions 👍

[mrossinek]

I would like to discuss this suggestion a bit more. Simply adding the eri as naive as I did here will imply very costly scaling.
Has the team around this schema thought about support for sparse matrices already?