L.G. Gutsev

Structure and Properties of Polyfluoride Fn– Clusters (n = 3–29)

The electronic and geometrical structures of the neutral Fn and singly negatively charged Fn(-) polyfluorides (n = 3-29) are studied using three levels of theory: density functional theory (DFT) with generalized gradient approximation, hybrid Hartree-Fock-DFT, and hybrid HF-DFT with long-range corrections. For n > 4, each polyfluoride possesses a number of states with different geometries that are closely spaced in total energy. The geometrical structures of the lowest total energy states follow different patterns for the even-n and odd-n Fn(-) anion branches with a preference for higher symmetry geometries. The largest F29(-) anion considered is found to possess Oh symmetry. All the anions beginning with F3(-) are found to possess adiabatic and vertical electron detachment energies exceeding the electron affinities of halogen atoms and are therefore superhalogen anions. Electron affinities, energies of formation, and binding energies show oscillatory behavior as functions of the number n of fluorine atoms. The neutral Fn species are found to be barely stable and are bound by polarization forces. The Fn(-) anions, on the contrary, are quite stable toward the loss of F, F(-), and F2(-), but not to the loss of F2.

A comparative study of small 3d-metal oxide (FeO)n, (CoO)n, and (NiO)n clusters

Geometrical and electronic structures of the 3d-metal oxide clusters (FeO)n, (CoO)n, and (NiO)n are computed using density functional theory with the generalized gradient approximation in the range of 1 ≤ n ≤ 10. It is found that the cluster geometries are similar in the (FeO)n and (CoO)n series but noticeably different in the (NiO)n series for several values of n. All of the lowest total energy states are found to possess relatively small spin multiplicities and are either antiferromagnetic or ferrimagnetic except for the states of (NiO)3, (NiO)4, (NiO)9, and (NiO)10, which are ferromagnetic. The computed polarizabilities per atom undergo a steep decrease when compared to the atomic values of the MO monomers (M = Fe, Co, and Ni). Surprisingly, the polarizability does not strongly depend on either M or n in all the considered series when n varies from 3 to 10. The binding energies per atom are the largest in the (FeO)n series, followed by the binding energies of (CoO)n and (NiO)n.

Structure and properties of iron oxide clusters: From Fe6 to Fe6O20 and from Fe7 to Fe7O24

Geometrical and electronic structures of the neutral and singly negatively charged Fe6On and Fe7Om clusters in the range of 1 ≤ n ≤ 20 and 1 ≤ m ≤ 24, respectively, are computed using density functional theory with the generalized gradient approximation. The largest clusters in the two series, Fe6O20 and Fe7O24, can be described as Fe(FeO4)5 and Fe(FeO4)6 or alternatively as [FeO5](FeO3)5 and [FeO6](FeO3)6, respectively. The Fe6O20 and Fe7O24 clusters possess adiabatic electron affinities (EAad) of 5.64 eV and 5.80 eV and can be attributed to the class of hyperhalogens since FeO4 is an unique closed‐shell superhalogen with the EAad of 3.9 eV. The spin character of the lowest total energy states in both series changes from ferromagnetic to ferrimagnetic or antiferromagnetic when the first FeOFe bridge is formed. Oxidation decreases substantially the polarizability per atom of the initial bare clusters; namely, from 5.98 Å3 of Fe6 to 2.47 Å3 of Fe6O20 and from 5.67 Å3 of Fe7 to 2.38 Å3 of Fe7O24. The results of our computations pertaining to the binding energies of O, Fe, O2, and FeO in the Fe7Om series provide an explanation for the experimentally observed abundance of the iron oxide nanoparticles with stoichiometric compositions.

Transitions From Stable to Metastable States in the Cr2On and Cr2On(-) Series, N = 1 - 14.

The geometrical and electronic structures of the Cr2On and Cr2On- clusters are computed using density functional theory with a generalized gradient approximation in the range of 1 ≤ n ≤ 14. Local total spin magnetic moments, polarizabilities, binding energies per atom, and energies of abstraction of O and O2 are computed for both series along with electron affinities of the neutrals and vertical detachment energies of the anions. In the lowest total energies states of Cr2O2, Cr2O3, Cr2O4, Cr2O14, Cr2O3-, Cr2O4-, and Cr2O14-, total spin magnetic moments of the Cr atoms are quite large and antiferromagnetically coupled. In the rest of the series, at least one of the Cr atoms has no spin-magnetic moment at all. The computed vertical electron-detachment energies of the Cr2On- are in good agreement with experimental values obtained in the 1 ≤ n ≤ 7 range. All neutral Cr2On possess electron affinities larger than the electron affinities of halogen atoms when n > 6 and are thus superhalogens. It is found that the neutrals and anions are stable with respect to the abstraction of an O atom in the whole range of n considered, whereas both neutrals and anions became unstable toward the loss of O2 for n > 7. The polarizability per atom decreases sharply when n moves from one to four and then remains nearly constant for larger n values in both series. The largest members in both series, Cr2O14 and Cr2O14-, possess the geometrical structures of the Cr2(O2)7 type by analogy with monochromium Cr(O2)4.

Modification of Magnetic Properties of Iron Clusters by Doping and Adsorption: From a Few Atoms to Nanoclusters

Electronic and geometrical structure of neutral and charged iron clusters Fe n , \({\text{Fe}}_{n}^{ - }\), and \({\text{Fe}}_{n}^{ + }\) (n = 2–20) will be discussed. Computational results will be compared to experimental data, in particular, to the recent data obtained from the magnetic moment measurements of \({\text{Fe}}_{n}^{ + }\). We consider iron cluster oxides, single Fe atom oxides FeO n for n up to 12, and FeX n superhalogens. We present the results of computational simulations of gas-phase interactions between small iron clusters and OH, N2, CO, NO, O2, and H2O. Competition between surface chemisorption and cage formation in Fe12O12 clusters will be discussed. The magnetic quenching found in Fe12O12 will be qualitatively explained using the natural bond orbital analysis performed on Fe2O2. Special attention will be paid to the structural patterns of carbon chemisorbed on the surface of a ground-state Fe13 cluster.