| The density functional theory which was first developed for solid-state calculations has been recently applied to a wide range of molecular electronic structure problems. In this work, this method is applied to study the structure and energetics of metal oxide clusters. The systems chosen, large clusters of magnesia, an alkaline earth oxide and microclusters of chromia, a transition metal oxide, were diverse in their size and electronic structure. Geometry optimization was performed on all the clusters to determine their minimum energy configuration within a given symmetry. Calculations on magnesia reveal the binding energy and near neighbor separation to show a progressive approach towards their corresponding bulk crystalline values with increasing cluster size. Charge density contours of the surface and inner layer show the presence of covalent effects on the surface of the 64 atom MgO cluster. In chromium oxide microclusters, the oxygen to metal ratio strongly influences the structural and electronic properties. Inclusion of non-local effects was found to be important to accurately determine the energies although reasonable structural configurations can be obtained using the local functionals. Ionization induced structural changes were found to be significant but were not found to affect the overall geometry of the clusters. The dissociation energy, bond length, dipole moment, vibrational frequency, ionization energy and the ground state electronic configuration of the neutral and ionized CrO molecule was found to be in excellent agreement with previous experimental and theoretical results. |
