A density functional theory investigation of the reactions of Fe and FeO2 with O2

• Published in: Computational materials science 2016-05, Vol.117, p.455-467
• Main Authors: Nakazawa, T., Kaji, Y.
• Format: Article
• Language: English
• Subjects: Conversion; Covalence; Density functional calculations; Density functional theory; Dioxides; Excitation; Fe + O2; Iron oxide; Mathematical analysis; OFeO + O2; Peroxides; Potential energy; Potential energy surface
• ISSN: 0927-0256; 1879-0801
• DOI: 10.1016/j.commatsci.2016.01.023

[Display omitted] •The reactions of an iron atom with oxygen molecules are studied by the DFT method.•Potential energy surfaces are calculated for the Fe+O2 and FeO2+O2 reactions.•In our calculations the reactions of Fe with O2 are found to be endothermic.•The FeO2+O2 reactions endothermically produce the η2-(O2)FeO2 and η1-(O2)FeO2.•Optimized structure, vibrational and NBO analyses for products are reported. The reactions of Fe and FeO2 with O2 and the products of these reactions are investigated at the B3LYP/6-311+G(d) level. The reactions are considered in terms of the calculated potential energy surfaces, the interaction energies between reactant species, and the energies required to populate the higher electronic states such as the excited states of Fe(5F, 3F) and O2(1Σg+). It is found that the reactions of Fe with O2 are endothermic and that the direct formation of dioxide OFeO is due to an ionic interaction of Fe+ with O2−. Furthermore, the diabatic transitions from the covalent and ionic surfaces onto another ionic surface with energy barriers allow the Fe+O2 reaction to proceed toward the formation of dioxide OFeO. There are other paths corresponding to the vertical excitation from peroxide Fe(O2) to dioxide OFeO; these require excitation energies above 23, 34, and 48kcalmol−1 in the low-lying triplet, quintet, and septet states, respectively. The OFeO+O2 reactions are found to endothermically produce the η2-(O2)FeO2 and η1-(O2)FeO2 complexes, and the low-lying states of complexes are found to be closely located in the energy range of 5.6kcalmol−1. The conversion of the η2-complex to the η1-complex and vice versa is caused by low energy. The NBO analyses show that the large atomic charges of peroxide Fe(O2), superoxide FeOO, and the η2- and η1-complexes are caused by electron transfer between reactant species, whereas those of dioxide OFeO are dominated by the ionic character of the species.