########################## 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 :doc:`ozone tutorial's <../ozone/automatically>` 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? 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 :download:`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 `_).