Dependence of Properties and Exchange Coupling Constants on the Charge in the Mn2On and Fe2On Series

The geometrical structure and properties of the neutral and singly charged Mn2Onq and Fe2Onq clusters (q = 0, ±1) are computed using density functional theory with the generalized gradient approximation in the range 1 ≤ n ≤ 7. The geometrical structures and spin multiplicities of the corresponding species in all six series are similar except for a few exceptions. Antiferromagnetic coupling of total spin magnetic moments of the metal atoms in the lowest total energy states is observed for the majority of species in all six series when n = 1-5; correspondingly, the computed magnetic exchange coupling constants are mostly negative. The states of Mn2Onq and Fe2Onq are nonmagnetic or weakly ferromagnetic when n > 5 except for Mn2O7+ where the ground state is antiferromagnetic. The computed adiabatic electron affinities and ionization energies of the neutral species in both series are quite close to one another and increase as n increases. However, the binding energies of a single oxygen atom and of an O2 dimer decrease as n increases and the Mn2O7+ and Fe2O7+ cations are barely stable with respect to the O2 abstraction. The most stable and least stable species at a given n are the anions and the cations, respectively. The electric dipole polarizability per atom decreases sharply when n moves from 1 to 4 and then remains nearly constant for larger n values in the anion series, whereas it is close to the asymptotic value already at n = 2 in the neutral series. Copyright © 2018 American Chemical Society

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. © 2017 American Chemical Society

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. © The Owner Societies 2016

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. © The Owner Societies 2016

Hydrogenation of 3d-metal oxide clusters: Effects on the structure and magnetic properties

The geometrical structures and properties of the M8O12, M8O12H8, and M8O12H12 clusters are explored using density functional theory with the generalized gradient approximation for all 3d-metals M from Sc to Zn. It is found that the geometries and total spin magnetic moments of the clusters depended strongly on the 3d-atom type and the hydrogenation extent. More than the half of all of the 30 clusters had singlet lowest total energy states, which could be described as either nonmagnetic or antiferromagnetic. Hydrogenation increases the total spin magnetic moments of the M8O12H12 clusters when MMnNi, which become larger by four Bohr magneton than those of the corresponding unary clusters M8. Hydrogenation substantially affects such properties as polarizability, forbidden band gaps, and dipole moments. Collective superexchange where the local total spin magnetic moments of two atom squads are coupled antiparallel was observed in antiferromagnetic singlet states of Fe8O12H8 and Co8O12H8, whereas the lowest total energy states of their neighbors Mn8O12H8 and Ni8O12H8 are ferrimagnetic and ferromagnetic, respectively. Hydrogenation leads to a decrease in the average binding energy per atom when moving across the 3d-metal atom series. © 2018 Wiley Periodicals, Inc. © 2018 Wiley Periodicals, Inc

Dependence of Properties and Exchange Coupling Constants on the Charge in the Mn2On and Fe2On Series

The geometrical structure and properties of the neutral and singly charged Mn2Onq and Fe2Onq clusters (q = 0, ±1) are computed using density functional theory with the generalized gradient approximation in the range 1 ≤ n ≤ 7. The geometrical structures and spin multiplicities of the corresponding species in all six series are similar except for a few exceptions. Antiferromagnetic coupling of total spin magnetic moments of the metal atoms in the lowest total energy states is observed for the majority of species in all six series when n = 1-5; correspondingly, the computed magnetic exchange coupling constants are mostly negative. The states of Mn2Onq and Fe2Onq are nonmagnetic or weakly ferromagnetic when n > 5 except for Mn2O7+ where the ground state is antiferromagnetic. The computed adiabatic electron affinities and ionization energies of the neutral species in both series are quite close to one another and increase as n increases. However, the binding energies of a single oxygen atom and of an O2 dimer decrease as n increases and the Mn2O7+ and Fe2O7+ cations are barely stable with respect to the O2 abstraction. The most stable and least stable species at a given n are the anions and the cations, respectively. The electric dipole polarizability per atom decreases sharply when n moves from 1 to 4 and then remains nearly constant for larger n values in the anion series, whereas it is close to the asymptotic value already at n = 2 in the neutral series. Copyright © 2018 American Chemical Society

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. © 2017 American Chemical Society

Evolution of properties in prolate (GaAs) n clusters

cited By 18International audienceThe structure and properties of prolate (GaAs)n clusters corresponding to the (2, 2) and (3, 3) armchair and (6, 0) zigzag capped single-wall tubes are studied using density functional theory with generalized gradient approximation (DFT-GGA). The largest number of atoms is 120 in the (2, 2) and (3, 3) series and 116 in the (6, 0) series. It is found that the band gap in all three series does not converge to the GaAs bulk value when the cluster length increases. The (2, 2) species has the smallest gaps, which are nearly 2 times smaller than the GaAs bulk gap at larger n. Cohesive energies per atom are found to be nearly independent of the cluster diameter and correspond to 75-78% of the bulk cohesive energy per atom. Special attention is paid to the static electric dipole polarizability and hyperpolarizability because conventional DFT-GGA methods provide satisfactory results only for clusters composed of less than ∼40 atoms. For larger clusters, conventional DFT polarizabilities and especially hyperpolarizabilities exhibit the divergent behavior. An inclusion of long-range corrections drastically changes this behavior and brings the corrected values close to the values obtained in the MP2 computations with the same basis sets. The CAM-B3LYP method recently devised to account for the long-range corrections was tested as well. Finally, we estimated asymptotic values for the (hyper)polarizabilies per unit length. © 2010 American Chemical Society