  Rubidium superoxide, RbO_2, is a rare example of a solid with
partially-filled electronic p states, which allows to study the interplay of
spin and orbital order and other effects of strong electronic correlations in a
material that is quite different from the conventional d or f electron systems.
Here we show, using a combination of density functional theory (DFT) and
dynamical mean-field theory, that at room temperature RbO_2 is indeed a
paramagnetic Mott insulator. We construct the metal-insulator phase diagram as
a function of temperature and Hubbard interaction parameters U and J. Due to
the strong particle-hole asymmetry of the RbO_2 band-structure, we find strong
differences compared to a simple semi-elliptical density of states, which is
often used to study the multiband Hubbard model. In agreement with our previous
DFT study, we also find indications for complex spin and orbital order at low
temperatures.
