HDF5 Hamiltonian generation and loading errors

[awoodwa]

A Hamiltonian saved to HDF5 on one environment cannot be loaded in another using Hamiltonian.from_hdf5_file. The load fails with:

ValueError: Tried to generate invalid Hamiltonian object.

Expected behavior

The Hamiltonian should load successfully across environments when using Hamiltonian.from_hdf5_file.

To Reproduce

Steps to reproduce the behavior:

1. Generate hdf5 file in one environment (envA) using qdk_chemistry version 2.0.0 (branch: feature/agamshayit/x2c0 ):

from qdk_chemistry.algorithms import create
from qdk_chemistry.data import Structure
from qdk_chemistry.utils import compute_valence_space_parameters
xyz = """3
Water molecule
O    0.000000    0.000000    0.000000
H    0.758602    0.000000    0.504284
H   -0.758602    0.000000    0.504284
"""
structure = Structure.from_xyz(xyz)
scf = create("scf_solver")
scf.settings().set("scf_type", "restricted")
e_scf, scf_wfn = scf.run(
    structure,
    charge=0,
    spin_multiplicity=1,
    basis_or_guess="def2-svp",
)
num_val_e, num_val_o = compute_valence_space_parameters(scf_wfn, charge=0)
selector = create("active_space_selector", "qdk_valence")
selector.settings().set("num_active_electrons", num_val_e)
selector.settings().set("num_active_orbitals", num_val_o)
active_wfn = selector.run(scf_wfn)
ham_constructor = create("hamiltonian_constructor", "qdk_cholesky")
ham_constructor.settings().set("cholesky_tolerance", 1e-6)
ham = ham_constructor.run(active_wfn.get_orbitals())
ham.to_hdf5_file("water.hamiltonian.h5")
print(f"SCF energy: {e_scf:.10f} Ha")
print(f"Valence active space: {num_val_e}e, {num_val_o}o")
print(f"Saved Hamiltonian: water.hamiltonian.h5")

2. Load hdf5 file in new environment (envB) where qdk_chemistry version 1.1.0 is used:

>>> from qdk_chemistry.data import Hamiltonian
>>> h = Hamiltonian.from_hdf5_file("water.hamiltonian.h5")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    h = Hamiltonian.from_hdf5_file("water.hamiltonian.h5")
ValueError: Tried to generate invalid Hamiltonian object.

Environments

Environment A (generation)

Field	Value
Machine	Intel Xeon Platinum 8180M
OS	Ubuntu
Python	3.12.3
qdk_chemistry	2.0.0 (feature/agamshayit/x2c0)

Environment B (loading)

Field	Value
Machine	AMD EPYC 7V12
OS	Azure Linux 3.0
Python	3.13.1
qdk_chemistry	1.0.0

Additional Notes:

• This error is not observed when generating the Hamiltonian via code provided in step 1 using envB, then reading on envA following the code provided in step 3
• hdf5 files generated in envA using qdk_chemistry version 2.0.0 can be properly loaded in another virtual environment on envA using qdk_chemistry version 1.1.0

Perhaps this is a python version discrepancy?