Long-range quantum computing (WF) in short-range DFT embedding

[stefabat]

This PR revamps the active space module and implements an embedding approach based on range-separated DFT.

An active space Hamiltonian describing a few electrons in a few orbitals embedded in the field of all remaining electrons is solved iteratively with external software.
The current implementation is interfaced to qiskit-nature, which enables the solution of the active space problem on classical and quantum hardware alike.

[oschuett]

It would be great to have an integration test for qiskit-nature. Maybe you could draft something akin to test_i-pi.sh or share an example input?

[fstein93]

This PR introduced a compilation issue. The moduel hdf5_wrapper has to check for __HDF5 (check cp2k_info for reference) and wrap the respective use statements and function bodies to prevent compilation errors if CP2K is not compiled with HDF5.

[stefabat]

It would be great to have an integration test for qiskit-nature. Maybe you could draft something akin to test_i-pi.sh or share an example input?

Yes, I can do that. I have another repo with many test examples and I can easily pull one or a few of them out.

[stefabat]

This PR introduced a compilation issue. The moduel hdf5_wrapper has to check for __HDF5 (check cp2k_info for reference) and wrap the respective use statements and function bodies to prevent compilation errors if CP2K is not compiled with HDF5.

You are right, I somehow completely forgot about hdf5_wrapper

[stefabat]

It would be great to have an integration test for qiskit-nature. Maybe you could draft something akin to test_i-pi.sh or share an example input?

Yes, I can do that. I have another repo with many test examples and I can easily pull one or a few of them out.

Actually, I first have to discuss with @mrossinek on how to do this, so it might take a few days before we have something similar in place.