  Many-body perturbation theory in the GW approach is applied to lanthanide
oxides, using the local-density approximation plus a Hubbard U correction
(LDA+U) as the starting point. Good agreement between the G0W0 density of
states and experimental spectra is observed for CeO2 and Ce2O3. Unlike the
LDA+U method G0W0 exhibits only a weak dependence on U in a physically
meaningful range of U values. For the whole lanthanide sesquioxide (Ln2O3)
series G0W0@LDA+U reproduces the main features found for the optical
experimental band gaps. The relative positions of the occupied and unoccupied
f-states predicted by G0W0 confirm the experimental conjecture derived from
phenomenological arguments.
