Density-functional investigations of the spin ordering in Fe₁₃ clusters

A recently developed two-step computational strategy [P. Bobadova-Parvanova et al., J. Chem. Phys. 116, 3576 (2002)] is used to investigate the geometric and magnetic properties of Fe₁₃. The method combines an unbiased search of the cluster energy surface using a density-functional-based tight-binding method, followed by fully self-consistent density-functional theory (DFT) calculations for detailed studies of the low-lying structures. The calculations indicate that the geometry of the Fe₁₃ cluster is a distorted icosahedron. Careful investigations of the optimal spin state of Fe₁₃ show the existence of two different magnetic orderings for the cluster - a ferromagnetically ordered state in which all atoms have approximately the same magnetic moment (3μ_B) and a nominally antiferromagnetic state in which the moment of the central atom is flipped with respect to those of the surface atoms. The relationship between cluster bond lengths and the magnetic ordering suggests that a transition in spin ordering could be driven by uniformly changing the geometric parameters in this cluster.