In this work, density functional theory (DFT) was used to obtain microscopic structures of heterogeneous catalysts based on rhodium supported on a metal oxide (-Al2O3). Two different methodologies were used. The first methodology uses a periodic model and a plane-wave basis set to solve the Schrödinger equation in the framework of Bloch’s theorem. The optimised structures of RhI(CO)2/ -Al2O3 species obtained at this level of theory have bond lengths in agreement with experimental EXAFS determinations. The weighted linear combination of Rh K-edge XANES spectra computed using the three most dominant structures reproduces well the phase and shape of the oscillations of the experimental XANES spectrum, providing support for the computed structures. The second methodology is based on hybrid quantum mechanical (QM)/molecular mechanical (MM) calculations. Within this scheme the support is described at the MM level of theory while the region of interest, the absorption site where the surface RhI(CO)2 complex lies, is described with a suitable QM approach. These hybrid calculations performed at the PBE/ECP/cc-pVDZ level of theory were used to obtainminimum-energy structures and harmonic stretching frequencies of RhI(CO)2/-Al2O3 species. The computed bond lengths and harmonic stretching frequencies were in good agreement with the experimental evidence and with the results obtained using periodic models.