A work is being done on the theoretical interpretation of spectra obtained in Metastable Impact Electron Spectroscopy (MIES) experiments. This work is being done in the collaboration with an experimental group at Clausthal University, Germany, lead by Prof. V. Kempter. There are two aspects in this work: (i) first of all, we have developed a general theory of MIES based on DFT description of the crystal surface electronic structure which has been applied to a clean MgO (001) surface and to a peroxide defect at it [B60,A6], and (b) a simpler version of the theory has been used for the study of Mg clusters formation on MgO surface using ab initio DFT calculations and MIES [B56].