First principles electronic structure investigations of the nature of adsorption, relaxation of the atoms near the adsorption site, and the charging of the Au2 particle on the relaxed-rumpled MgO(100) surface have been carried out within the density functional theory-cluster-embedding approach. The investigations focus on an Au2 molecule, perpendicular to the surface, adsorbed at different locations. Three bonding sites are studied: a five coordinated oxygen regular terrace site O5c, an Fs neutral color center (two electrons in an O vacancy), and an F+s positive charged color center (one electron in an O vacancy). The studies indicate that large relaxation of the neighboring atoms and large charge transfer occurs for an Au2 over the color centers. An analysis of the one-electron energy levels of the Au dimer, the MgO surface and the Au2MgO(100) complex for each absorption site allows us to rationalize the nature of the bonding, surface relaxation, calculated absorption and dimerization energies and electron charge transfers.First principles electronic structure investigations of the nature of adsorption, relaxation of the atoms near the adsorption site, and the charging of the Au2 particle on the relaxed-rumpled MgO(100) surface have been carried out within the density functional theory-cluster-embedding approach. The investigations focus on an Au2 molecule, perpendicular to the surface, adsorbed at different locations. Three bonding sites are studied: a five coordinated oxygen regular terrace site O5c, an Fs neutral color center (two electrons in an O vacancy), and an F+s positive charged color center (one electron in an O vacancy). The studies indicate that large relaxation of the neighboring atoms and large charge transfer occurs for an Au2 over the color centers. An analysis of the one-electron energy levels of the Au dimer, the MgO surface and the Au2MgO(100) complex for each absorption site allows us to rationalize the nature of the bonding, surface relaxation, calculated absorption and dimerization energies and electron charge transfers.