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Coal and oil combustion produces fly ash particulates whose dispersion into the environment represents one of the major sources of pollution.

The X-Ray Photoemission (XP) core level spectra of transition metal (TM) compounds have been intensively investigated with the aim to obtain appropriate parameters to characterise their electronic properties 1–15. In particular, the charge transfer (CT) energy, A, which describes the charge fluctuation from the ligand to the metal according to the mechanism d n → d n+1 L and the Mott-Hubbard energy U, which accounts for the electronic charge fluctuation between two transition metal ions in the crystal lattice, \( d_i^nd_j^n \to d_i^{n - 1}d_j^{n + 1} \) are basic concepts to understand the electronic correlations of TM compounds 7–9.

After the discovery of the cuprate superconductors1 the elctronic structure of 3d-transition metals (TM) compounds became a focal point in solid state physics. Particularly, long standing questions regarding the physics of correlation effects are, nowadays, one of the more important issues to be addressed in order to understand the electronic mechanisms that are responsable for the superconducting phenomena2. An appropriate description of the electronic structure of late (Mn-Cu) 3d TM compounds does not exist and different approaches are used to interpret particular behavior of these compouds. The one electron-band picture, which ignores the correlation effects by using an average potential, gives results in contradiction with the experiments. Discrepancy, reported first by Boer and Verwey3, was partially resolved by Mott4 and Hubbard5. They pointed out that if the exchange and Coulomb energies (U), involved in charge fluctuations between d-orbitals of TM ions in different sites, are larger than the one-electron dispersion with band width (w), the one-electron description of solids is expected to break down.

It is widely recognized that an understanding of the physical and chemical properties of clusters will give a great deal of important information relevant to surface and bulk properties of condensed matter. This relevance of clusters for condensed matter is one of the major motivations for the study of atomic and molecular clusters. The changes of properties with cluster size, from small clusters containing only a few atoms to large clusters containing tens of thousands of atoms, provides a unique way to understand and to control the development of bulk properties as separated units are brought together to form an extended system. Another important use of clusters is as theoretical models of surfaces and bulk materials. The electronic wavefunctions for these cluster models have special advantages for understanding, in particular, the local properties of condensed matter. The cluster wavefunctions, obtained with molecular orbital theory, make it possible to relate chemical concepts developed to describe chemical bonds in molecules to the very closely related chemical bonding at the surface and in the bulk of condensed matter. The applications of clusters to phenomena in condensed matter is a cross-disciplinary activity which requires the interaction and collaboration of researchers in traditionally separate areas. For example, it is necessary to bring together workers whose background and expertise is molecular chemistry with those whose background is solid state physics. It is also necessary to bring together experimentalists and theoreticians.