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A density-functional study of the structures, binding energies and magnetic moments of the clusters MoN (N = 2–13), Mo12Fe, Mo12Co and Mo12Ni

We report the results of density-functional calculations of the structures, binding energies and magnetic moments of the clusters MoN (N = 2–13), Mo12Fe, Mo12Co and Mo12Ni that were performed using the SIESTA method within the generalized gradient approximation for exchange and correlation. For pure MoN clusters, we obtain collinear magnetic structures in all cases, even when the self-consistent calculations were started from non-collinear inputs. Our results for these clusters show that both linear, planar and three-dimensional clusters have a strong tendency to form dimers. In general, even-numbered clusters are more stable than their neighbouring odd-numbered clusters because they can accommodate an integer number of tightly bound dimers. As a consequence, the binding energies of pure MoN clusters, in their lowest-energy states, exhibit an odd–even effect in all dimensionalities. Odd–even effects are less noticeable in the magnetic moments than in the binding energies. When comparing our results for pure Mo clusters with those obtained recently by other authors, we observe similarities in some cases, but striking differences in others. In particular, the odd–even effect in three-dimensional Mo clusters was not observed before, and our results for some clusters (e.g. for planar Mo3 and Mo7 and for three-dimensional Mo7 and Mo13) differ from those reported by other authors. For Mo12Fe and Mo12Ni, we obtain that the icosahedral configuration with the impurity atom at the cluster surface is more stable than the configuration with the impurity at the central site, while the opposite occurs in the case of Mo12Co. In Mo12Co and Mo12Ni, the impurities exhibit a weak magnetic moment parallely coupled to the total magnetic moment of the Mo atoms, whereas in Mo12Fe the impurity shows a high moment with antiparallel coupling.