  We present high accuracy relativistic coupled cluster calculations of the
first and second ionisation potentials and the electron affinity of the
heaviest element in the Periodic Table, Og. The results were extrapolated to
the basis set limit and augmented with the higher order excitations (up to
perturbative quadruples), the Breit contribution, and the QED self energy and
vacuum polarisation corrections. We have performed an extensive investigation
of the effect of the various computational parameters on the calculated
properties, which allowed us to assign realistic uncertainties on our
predictions. Similar study on the lighter homologue of Og, Rn, yields excellent
agreement with experiment for the first ionisation potential and a reliable
prediction for the second ionisation potential.
