The favorable stoichiometry of Co(n)O(m)(+) clusters has been recently determined by means of multiphoton dissociation of oxide cluster beams coming from laser evaporation of metal rods seeded with 0.5-5% oxygen and selected by time of flight mass spectroscopy. It was observed that the prominent stoichiometry is n = m, and that the preferred dissociation channel is the loss of O2 molecules. The Co4O4(+) cluster is found to be particularly abundant, an indication of its high stability. In this work we present density functional calculations, within the generalized gradient approximation, for the geometric, electronic, and magnetic properties of neutral and cationic Co(n)O(m)(0/+) clusters with n = 3-8 and m = 1-10. The ionic structures were determined after optimizing several initial geometries selected from previous calculations of pure Co clusters, with consecutive adsorbed oxygen atoms, as well as geometries constructed by assembling several CoO units and adding subsequent oxygen atoms. The fragmentation patterns were studied by comparing the energy separation of O2, CoO, Co2O, CoO2, and Co fragments. We obtain that the preferred fragmentation channel is the loss of O2, that the favourable stoichiometry is 1 : 1, and that Co4O4(+) is especially stable, in full agreement with the experiments. In addition the magnetic properties related to spin isomeric configurations of (CoO)n(+) clusters are studied in detail.

We performed standard and van der Waals-corrected density functional theory calculations to investigate the hydrogen storage capacity of a phase of borophene with Pmmn symmetry and nonzero thickness. This borophene sheet (Pmmn8) has 8 atoms in its unit cell and is more stable than the planar α sheet and that the corrugated Pmmn2 sheet (2 atoms in the unit cell). Our results show that, in pristine form, the Pmmn8 sheet is not suited for hydrogen storage applications. However, decoration with Li atoms and strain increase the hydrogen storage ability of the sheet. We performed also a detailed quantum chemical topological analysis that shows that the B-Li interaction in the hydrogenated Li-decorated Pmmn8 sheet is ionic. Our results for the adsorption of H 2 on the Li-decorated Pmmn8 sheet are compared with those obtained for the adsorption of H 2 on Ti-decorated zigzag graphene nanoribbons.

We report a comprehensive theoretical study of the structural and electronic properties of neutral and charged nickel oxide clusters, NiO (n = 3-8 and m = 1-10), in the context of recent experiments of photodissociation and Ion Mobility Mass Spectrometry. By means of density functional theory calculations in the generalized gradient approximation for exchange and correlation, we determined the putative ground states as well as the low-energy structural- and spin-isomers which were then used to explore the favorable fragmentation channels of the nickel oxide cationic clusters, and the resulting most abundant products, in good qualitative agreement with photodissociation measurements. Apart from stoichiometries different from those of their nickel oxide macroscopic counterparts, we found a tendency to form compact Ni subclusters, with reentrance of low-coordinated structures close to the equiatomic Ni-O concentration, taking the form of alternating Ni-O rings in the smaller sizes, in good qualitative agreement with Ion Mobility Mass Spectrometry measurements. This structural pattern is manifested in a drop of the total spin magnetic moment close to the equiatomic concentration due to the formation of antiparallel magnetic couplings. Although antiparallel couplings are found to a more or less extent in most clusters, especially in the oxygen rich phase, we identified certain clusters of special interest in the context of magnetic grains because of their large total magnetic moment and abundance. There are even some nickel oxide clusters with a higher total moment than their pure Ni counterparts, due to parallel magnetic couplings and the contribution of the oxygen atoms to the total moment.