The IP and EA of ozone

This tutorial calculates the ionization potential (IP) and electron affinity (EA) of the ozone molecule with the KI functional. Both are quantities a photoemission experiment measures directly — the energy to remove an electron from the highest occupied molecular orbital (HOMO), and the energy gained by adding one to the lowest unoccupied molecular orbital (LUMO) — and both are quantities that ordinary density-functional theory gets badly wrong. A Koopmans calculation reads them off the orbital energies of the corrected functional, with screening parameters computed from first principles.

The tutorial comes in two parts. The first runs the calculation manually, one Quantum ESPRESSO command at a time, and computes a single screening parameter with a pen-and-paper formula. The second hands the whole procedure to koopmans, which does all of these calculations automatically.