Systematic theoretical investigation of geometries, stabilities and magnetic properties of iron oxide clusters (FeO)nμ (n=1-8, μ=0, ±1): insights and perspectives

The structural properties of neutral and charged (FeO)(n)(mu) (n = 1-8, mu = 0, +/- 1) clusters have been studied using an unbiased CALYPSO structure searching method. As a first step, an unbiased search relying on several structurally different initial clusters has been undertaken. Subsequently, geometry optimization by means of density-functional theory with the Perdew and Wang (PW91) exchange-correlation functional is carried out to determine the relative stability of various candidates for low-lying neutral, anionic and cationic iron oxide clusters obtained from the unconstrained search. It is shown that the mostly equilibrium geometries of iron oxide clusters represent near planar structures for n <= 3. No significant structural differences are observed between the neutral and charged iron oxide clusters beyond sizes with n = 6. The relative stabilities of (FeO)(n)(mu) clusters for the ground-state structures are analyzed on the basis of binding energies and HOMO-LUMO gaps. Our theoretical results confirm that the binding energies of neutral and anionic (FeO)(n)(0/-) tend to increase with cluster size. Cationic (FeO)(n)(+) exhibits a slight downward trend. It is worth noticing that (FeO)(5) and (FeO)(4)(-/+) are the most stable geometries for (FeO)(n)(mu) (n = 1-8, mu = 0, +/- 1) clusters. Lastly, an evident local oscillation of magnetic behavior is present in the most stable (FeO)(n)(mu) (n = 1-8, mu = 0, +/- 1) clusters, and the origin of this magnetic phenomenon is analyzed in detail.