Evolution of Ferromagnetic and Antiferromagnetic States in Iron Nitride Clusters FeN and FeN ( = 1-10).

First-principles density functional theory calculations on neutral and singly negatively and positively charged iron clusters Fe and iron nitride clusters FeN and FeN ( = 1-10) in the range of 1 ≤ ≤ 10 revealed that there is a strong competition between ferromagnetic and antiferromagnetic states especially in the FeN cluster series. This phenomenon was related to superexchange via a bridging N atom between two iron atoms in the FeN cluster series and to a double superexchange effect via a Fe atom shared by two N atoms in the FeN series. A thorough examination of the structure-energy-spin state relationships in these clusters is conducted, leading to new insights and confirmation of available experimental results on structural parameters and dissociation energetics. The bond energies of both nitrogen atoms in the FeN series are approximately the same. They weakly depend on the charge of the host cluster and fluctuate around 5.5 eV when moving along the series. The energy of N desorption is relatively small; it varies by about 1.0 eV and depends on the charge of the cluster. The experimental finding that N dissociates on the Fe clusters beginning with = 4 was supported by the results of our computations. Our computed values of the Fe-N bonding energies agree with the experimental data within the experimental uncertainty bars. It was found that the attachment of one or two N atoms does not seriously affect the polarizability, electron affinity, or ionization energy of the host iron clusters independent of the charge.