Role of the exchange and correlation interactions on the electronic and magnetic properties of small iron-oxide clusters

By utilizing the Becke 3-parameter Lee-Yang-Parr (B3LYP) hybrid ex-change-correlation(XC) functional, which combines both local and non-local exchange-correlation terms, we conduct first-principles calculations to investigate the electronic, magnetic, and structural properties of small iron-oxide clusters (with N ≤ 8). Additionally, we employ the semi-local Perdew-Burke-Ernzerhof (PBE) XC-functional along with the PBE+U approximation, which accounts for on-site intra-atomic Coulomb repulsion interactions. We compare the results with those obtained using the non-local functional. Our findings show that the choice of the XC-functional strongly influences the physical properties of the iron-oxide clusters. The clusters adopt planar structures with Fe-O-Fe bonding angles close to 90◦ degrees, facilitating the emergence of indirect or super-exchange interaction mechanisms between the Fe-atoms mediated by the connecting oxygen atoms. Overall, the stabilization of the magnetic ordering is driven by the competition between direct and indi-rect exchange interactions, with the latter favoring antiferromagnetism. A Local Density of States (LDOS) together with a Crystal Orbital Hamilton Population(COHP) analysis allows us to identify the symmetries of the participating d-orbitals on these interaction mechanisms from a local perspective, which control the magnetic properties of the iron-oxide clusters. Besides, our results highlight the importance of using XC-functionals that more accurately account for exchange and electronic correlation interactions rather than relying solely on standard semi-local functionals.