TREXIO + MCSCF wavefunction

[NastaMauger]

Hello,

In this PR, you will find modifications that allow users to register an MCSCF function in the TREXIO format.

I am uncertain if additional data must be stored for TREXIO to function correctly with other software and to return the corresponding wave function produced by PySCF before registering it into TREXIO. However, the corresponding HDF5 file generated using the following code:

mcscf = mcscf.casci_symm.CASCI(rhf, norb, nelec)
mcscf.fcisolver = selected_ci_spin0_symm.SelectedCI(rhf)

mcscf.kernel()
trexio_file = 'data_mcscf.hdf5'
pyscf_trexio.to_trexio(mcscf, trexio_file)

pyscf_trexio.det_to_trexio(mcscf, norb, nelec, trexio_file)
eri = mol.intor('int2e')
pyscf_trexio.write_eri(eri, trexio_file)

seems to register the data correctly.

Please let me know if further modifications or improvements are necessary. I am also uncertain whether the one-electron MO group is essential, as mentione here. I would also appreciate any feedback on whether the write_eri function needs to be modified to handle CASCI/CASSCF, particularly for the corresponding active space

Best

[q-posev]

Thank you @NastaMauger !

I noticed that you do not register the CI determinants as part of your new mcscf_to_trexio. Is it intended?

[q-posev]

I guess the best test of the validity of the produced multi-configurational TREXIO wavefunction is via an attempt to import and use it in some software that handles such wave functions (e.g. QP2)? @NastaMauger @scemama

[q-posev]

Why is this removed? We need the number of up and down electrons to perform the CI determinants "correctness" check before writing them in the file.