TIGHT-BINDING STUDY OF THE IONIZATION OF IRON CLUSTERS

A microscopic calculation of the ionization potential of ferromagnetic Fe-N clusters (3 less than or equal to N less than or equal to 89) ha s been performed. The spin-polarized electronic structure is calculate d by self-consistently solving a tight-binding Hamiltonian for the 3d, 4s, and 4p valence electrons. Different isomers (open and compact, sy mmetric and asymmetric) are considered for N less than or equal to 8. As a general trend, the extracted electron has the d character of mino rity spin orbitals mainly located in the outer atomic shells. Good agr eement with experiment has been obtained for N less than or equal to 7 using structures taken from ab initio molecular dynamics simulations and for N greater than or equal to 23 using bcc-like structures. The e ffects of the geometry and of the relaxation of the interatomic distan ces have been studied for N < 8. The results for bcc structures in the intermediate-size range (8 < N < 23) are not satisfactory.