Electronic Structure and Properties of FeO_n and FeO_n^- Clusters

Abstract

The electronic and geometrical structures of the ground and some excited states of the FeO n and FeO n - clusters (n = 1−4) have been calculated using the density-functional theory with generalized gradient approximation for the exchange-correlation potential. It is found that the multiplicity of the ground states decreases with increasing n, and the ground states of FeO- and FeO2 - are quartets whereas those of FeO3 - and FeO4 - are doublets. All of these anions possess isomers with different spatial or spin symmetries that are close in energy to their ground states. For example, FeO4 - has at least five stationary states that are stable against electron detachment and fragmentation. Our calculated adiabatic electron affinities (A ad) of FeO, FeO2, and FeO3 are within 0.2 eV of the experiment. FeO4 was found to be a particularly interesting cluster. Although its neutral precursor possesses a closed electronic shell structure, it has an A ad of 3.8 eV, which is higher than the electronic affinity of halogen atoms. The experimental estimate of 3.3 eV for the A ad of FeO4 is shown to originate from the detachment of an electron from one of the higher-energy isomers of the FeO4 - cluster. The energetically preferred dissociation channels of FeO2, FeO3, FeO4, FeO3 -, and FeO4 - correspond to abstraction of an O2 dimer but not to an Fe−O bond rupture. FeO3 - and FeO4 - are found to be thermodynamically more stable than their neutral closed-shell parents, and FeO3 - is the most stable of all the clusters studied. The existence of several low-lying states with different multiplicities in FeO n and FeO n - indicates that their magnetic properties may strongly depend on temperature.

Quantum Monte Carlo study of the ground state and low-lying excited states of the scandium dimer

“…[16][17][18][19][20][21] In general, these studies predicted bond lengths in the range of 2.55-2.70 Å and frequencies that are in good agreement with the corresponding experimental marks. The calculated ionization energy of Sc was also in agreement with the experimental value of 6.56 eV.…”

Ground and low‐lying excited C2v states of FeO2—A challenge to computational methods

“…All methods agree on the symmetry of the lowest state of each spin multiplicity, with the lowest singlet being Optimized geometries and adiabatic excitation energies of all lowest states, the lowest A 1 , A 2 , B 1 , and B 2 states of each spin multiplicity, are given in Table II [2]. In several cases optimizations with orbital promotion led to states lower in energy than the "lowest" states in Table I that were obtained without orbital promotion.…”

“…Gutsev et al [2] performed extensive DFT (BPW91/6-311ϩG*) studies on the FeO n and FeO n Ϫ molecules (n ϭ 1-4). Geometries, energies and vibrational frequencies for the 1 In two previous papers in this series, optimized geometries and other properties of low-lying singlet, triplet, and quintet excited states of TiO 2 [9] and CrO 2 [10] MRCI calculations were performed with the Grimme-Waletzke programs [13,14].…”

Manganese, Iron, Cobalt, and Nickel Oxo‐, Peroxo‐, and Superoxoclusters: A Density Functional Theory Study

“…The dissociation energy of NiO is underestimated by 0.65 eV by the B1LYP method. The BPW91, which has been used in a number of studies of transition-metal oxoclusters, [17,26] shows inferior performance, because the bond lengths of MnO and NiO differ significantly from experimental data, and the dissociation energies are overestimated by about 1 eV.…”