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

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We report the results of density-functional calculations of thestructures, binding energies and magnetic moments of the clustersMoN (N = 2–13), Mo12Fe, Mo12Co and Mo12Ni that were performed using the SIESTA method within the generalizedgradient approximation for exchange and correlation. For pureMoN clusters, we obtain collinear magnetic structures in all cases, even when the self-consistentcalculations were started from non-collinear inputs. Our results for these clusters showthat both linear, planar and three-dimensional clusters have a strong tendencyto form dimers. In general, even-numbered clusters are more stable than theirneighbouring odd-numbered clusters because they can accommodate an integernumber of tightly bound dimers. As a consequence, the binding energies of pureMoN 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 bindingenergies. When comparing our results for pure Mo clusters with those obtainedrecently by other authors, we observe similarities in some cases, but strikingdifferences in others. In particular, the odd–even effect in three-dimensional Moclusters was not observed before, and our results for some clusters (e.g. for planarMo3 andMo7 and forthree-dimensional Mo7 and Mo13) differ from those reported by other authors. ForMo12Fe and Mo12Ni, we obtain that the icosahedral configuration with the impurity atomat the cluster surface is more stable than the configuration with theimpurity at the central site, while the opposite occurs in the case ofMo12Co.In Mo12Co and Mo12Ni, the impurities exhibit a weak magnetic moment parallely coupledto the total magnetic moment of the Mo atoms, whereas inMo12Fe the impurity shows a high moment with antiparallel coupling.