Explanation of the Invar Anomalies from Molecular-Orbital Cluster Calculations

The electronic structures of pure and mixed Fe-Ni metal clusters, as computed with the self-consistent-field $X\alpha$ scattered-wave method, are used as models for the bonding situation in fcc Fe-Ni alloys. The calculations indicate that several anomalous properties of the Invar alloy ${\mathrm{Fe}}_{64}$ ${\mathrm{Ni}}_{36}$ are a consequence of the presence, at the Fermi level, of strongly antibonding majority-spin orbitals and nonbonding minority-spin orbitals in this concentration range.