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Spin-polarized molecules

A molecule with an open shell: the oxygen molecule, whose ground state is a spin triplet. Treating the two spin channels separately changes what a Koopmans calculation is working with — every orbital now carries a spin channel as well as an index, and it gets its own screening parameter — so this tutorial is the closed-shell ozone calculation again, with that difference drawn out. The screening parameters come from total-energy differences.

Note

This tutorial has not been written yet. It is tracked by issue #75.

A challenge in the meantime: modify the ozone tutorial’s input file for molecular oxygen, and see whether the IP and EA compare as well to experiment. O₂ is a linear molecule with a bond length of 1.21 Å, and — unlike ozone — it is paramagnetic, so its two spin channels differ.

Question

Do the IP and EA of O₂ compare as well to experiment?

Show answer

Set spin: collinear in the workflow block, add tot_magnetization: 2 and lower nbnd to 8 in calculator_parameters, and update the atoms. A complete input file — which also runs two screening iterations and lets near-degenerate orbitals share a screening parameter — is o2.yaml. Running it gives an IP of 12.35 eV and an EA of 0.40 eV, against experimental values of 12.07 and 0.45 eV (NIST).