Ab initioSimulations of Fe and TiC clusters

Iron clusters of bcc, fcc and icosahedral structure, up to the largest Fe59 (bcc), Fe55 and Fe62 (atom- and interstitial-centered fcc), Fe55 (icosahedral), and titanium carbide (Ti4 C4, Ti14 C13) were relaxed, within the given morphology type, on the basis of first-principles calculation in the density functional theory, using norm-conserving pseudopotentials and a basis set of strictly localized numerical functions. For TiC, moreover, the vibrational spectrum has been studied in a molecular dynamics approach. The results show inward relaxation at the cluster surface, accompanied by the enhancement of local magnetic moments in several surface layers up to ∼3 μB (in Fe), or by hardening of the Γ-TO phonon mode (in TiC).