DENSITY-FUNCTIONAL STUDY OF CHROMIUM-OXIDE CLUSTERS - STRUCTURES, BONDING, VIBRATIONS, AND STABILITY

We report the results of density functional theory calculations on chr omium oxide clusters responding to the formula CrmOn (m = 1-2, n = 1-3 ). Double numeric basis sets supplemented by polarization functions ha ve been used in both local and nonlocal spin density approximations. G eometry optimizations of different spin states have been performed at the unrestricted spin level for the selected initial configurations. W e have found that the covalent polarized Cr-O bonds dominate the chemi cal description of the CrOn series, while for the Cr2On series the pre sence of the Cr-Cr bond reduces the metal to oxygen charge transfer, y ielding much softer clusters, as reflected by the smaller HOMO-LUMO ga ps. The stability of all the isomers has been checked by computing the ir harmonic vibrational frequencies and the energetics of different fr agmentation paths. The calculations reveal that the linear isomers are not true minima and that the oxygen-rich clusters are preferred over the metal-rich clusters. Overall, our results show good agreement with the available experimental data in terms of geometrical parameters, v ibrational frequencies, atomization energies, and fragmentations for t he CrOn clusters. For the Cr2O series, our computed values are discuss ed in connection with recent infrared spectroscopy measurements and wi th available data in analogous metal oxide clusters.