Using density functional theory with generalized gradient approximation, we have performed a systematic study of the structure and properties of neutral and charged trioxides (MO(3)) and tetraoxides (MO(4)) of the 3d-metal atoms. The results of our calculations revealed a number of interesting features when moving along the 3d-metal series. (1) Geometrical configurations of the lowest total energy states of neutral and charged trioxides and tetraoxides are composed of oxo and∕or peroxo groups, except for CuO(3)(-) and ZnO(3)(-) which possess a superoxo group, CuO(4)(+) and ZnO(4)(+) which possess two superoxo groups, and CuO(3)(+), ZnO(3)(+), and ZnO(4)(-) which possess an ozonide group. While peroxo groups are found in the early and late transition metals, all oxygen atoms bind chemically to the metal atom in the middle of the series. (2) Attachment or detachment of an electron to∕from an oxide often leads to a change in the geometry. In some cases, two dissociatively attached oxygen atoms combine and form a peroxo group or a peroxo group transforms into a superoxo group and vice versa. (3) The adiabatic electron affinity of as many as two trioxides (VO(3) and CoO(3)) and four tetraoxides (TiO(4), CrO(4), MnO(4), and FeO(4)) are larger than the electron affinity of halogen atoms. All these oxides are hence superhalogens although only VO(3) and MnO(4) satisfy the general superhalogen formula.

The electronic and geometrical structures of the Fe(n), Fe(n)(–), and Fe(n)(+) series (n = 7–20) are studied using all-electron density functional theory with the generalized gradient approximation. Equilibria of the geometrical configurations of the lowest total energy states in all three series are found to be similar except for Fe(9)(–), Fe(9)(+), Fe(10)(–), Fe(10)(+), Fe(15)(–), and Fe(19)(+). Our computed ionization energies of the neutrals, vertical electron detachment energies, and energies of Fe atom abstraction are in good agreement with experiment. It is found that the one-electron model corresponding to the change in the total magnetic moment of ±1.0μ(B) due to either attachment or detachment of an electron is valid in most cases. The exceptions are Fe(4)(+), Fe(10)(–), Fe(10)(+), Fe(12)(–), Fe(13)(+), and Fe(14)(+), where the change in the total magnetic moment is +3μ(B) (Fe(10)(–) and Fe(12)(–)), −3μ(B) (Fe(4)(+), Fe(11)(+), and Fe(14)(+)), and −9μ(B) (Fe(13)(+)). The reason for an anomalously large quenching of the total spin magnetic moment in Fe(13)(+) is explained. Our computed total spin magnetic moments per atom match the recent experimental values within the experimental uncertainty bars.

The geometrical and electronic structures of Al(BO(2))(n) and Al(BO(2))(n)(-) (n = 1-4) clusters are computed at different levels of theory including density functional theory (DFT), hybrid DFT, double-hybrid DFT, and second-order perturbation theory. All aluminum borates are found to be quite stable toward the BO(2) and BO(2)(-) loss in the neutral and anion series, respectively. Al(BO(2))(4) belongs to the class of hyperhalogens composed of smaller superhalogens, and should possess a large adiabatic electron affinity (EA(ad)) larger than that of its superhalogen building block BO(2). Indeed, the aluminum tetraborate possesses the EA(ad) of 5.6 eV, which, however, is smaller than the EA(ad) of 7.8 eV of the AlF(4) supehalogen despite BO(2) is more electronegative than F. The EA(ad) decrease in Al(BO(2))(4) is due to the higher thermodynamic stability of Al(BO(2))(4) compared to that of AlF(4). Because of its high EA and thermodynamic stability, Al(BO(2))(4) should be capable of forming salts with electropositive counter ions. We optimized KAl(BO(2))(4) as corresponding to a unit cell of a hypothetical KAl(BO(2))(4) salt and found that specific energy and energy density of such a salt are competitive with those of trinitrotoluol (TNT).

The electronic and geometrical structures of oxygen-rich neutral and negatively charged FeO(5), FeO(6), FeO(7), FeO(8), FeO(9), FeO(10), FeO(11), and FeO(12) clusters were obtained using density functional theory with generalized gradient approximation. With the exception of FeO(11) and FeO(12), all clusters are found to possess a large number of isomers composed of oxo, peroxo, superoxo, and ozonide fragments that are closely spaced in total energy, especially for n = 7 and 8. The preferable structures of FeO(12) are composed of superoxo groups with different orientations. All the neutral species possess rather large electron affinities, which range from 3.24 eV (FeO(8)) to 3.95 eV (FeO(5)). Although all of the lowest energy states were found to possess positive vibrational frequencies and thus are geometrically stable, the states are thermodynamically unstable against dissociation to FeO(4) + (n - 4)/2 O(2) for n = 6, 8, 10, and 12 and FeO(5) + (n - 5)/2 O(2) for n = 7, 9, and 11. In particular, the decay of FeO(12) is exothermic by 34 kcal/mol.