Density functional calculations of the electronic structure of the Fe12 cluster encapsulated inside finite singlewall\udzigzag carbon nanotubes of indices (11,0) and (10,0) have been performed. Several Fe12 isomers have\udbeen considered, including elongated shape isomers aimed to fit well inside the nanotubes, and the icosahedral\udminimum energy structure. We analyze the structural and magnetic properties of the combined systems, and\udhow those properties change compared to the isolated systems. A strong ferromagnetic coupling between the\udFe atoms occurs both for the free and the encapsulated Fe12 clusters, but there is a small reduction (3–7.4μB)\udof the spin magnetic moment of the encapsulated clusters with respect to that of the free ones (μ = 38μB).\udThe reduction of the magnetic moment is mostly due to the internal redistribution of the spin charges in the\udiron cluster. In contrast, the spin magnetic moment of the carbon nanotubes, which is zero for the empty tubes,\udbecomes nonzero (1–3μB) because of the interaction with the encapsulated cluster. We have also studied the\udencapsulation of atomic Fe and the growth of small Fen clusters (n = 2, 4, 8) encapsulated in a short (10,0) tube.\udThe results suggest that the growth of nanowires formed by distorted tetrahedral Fe4 units will be favorable in\ud(10,0) nanotubes and nanotubes of similar diameter.
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