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Nanomaterials made of the cerium oxides CeO$_2$ and Ce$_2$O$_3$ have a broadrange of applications, from catalysts in automotive, industrial or energyoperations to promising materials to enhance hadrontherapy effectiveness inoncological treatments. To elucidate the physico-chemical mechanisms involvedin these processes, it is of paramount importance to know the electronicexcitation spectra of these oxides, which are obtained here throughhigh-accuracy linear-response time-dependent density functional theorycalculations. In particular, the macroscopic dielectric response functions$\bar\epsilon$ of both bulk CeO$_2$ and Ce$_2$O$_3$ are derived, which compareremarkably well with the available experimental data. These results stress theimportance of appropriately accounting for local field effects to model thedielectric function of metal oxides. Furthermore, we reckon the materialsenergy loss functions $\mbox{Im} (-1/\bar{\epsilon})$, including the accurateevaluation of the momentum transfer dispersion from first-principles. In thisrespect, by using a Mermin-type parametrization we are able to model thecontribution of different electronic excitations to the dielectric lossfunction. Finally, from the knowledge of the electron inelastic mean free path,together with the elastic mean free path provided by the relativistic Motttheory, we carry out statistical Monte Carlo (MC) charge transport simulationsto reproduce the major features of the reported experimental reflectionelectron energy loss (REEL) spectra of cerium oxides. The good agreement withREEL experimental data strongly supports our approach based on MC modellinginformed by ab initio calculated electronic excitation spectra in a broad rangeof momentum and energy transfers.

Electronic excitation spectra of cerium oxides: from ab initio dielectric response functions to Monte Carlo charge transport simulations