Transitions from Stable to Metastable States in the Cr₂O_n and Cr₂O_n^– Series, n = 1–14

Abstract

The geometrical and electronic structures of the CrO and CrO 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 O 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 CrO, CrO, CrO, CrO, CrO, CrO, and CrO, 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 CrO are in good agreement with experimental values obtained in the 1 ≤ n ≤ 7 range. All neutral CrO 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 O 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, CrO and CrO, possess the geometrical structures of the Cr(O) type by analogy with monochromium Cr(O).

Increased Excited State Metallicity in Neutral Cr2On Clusters (n < 5) Upon Sequential Oxidation

“…Additionally, chromium oxide clusters may be uniquely suitable for spintronics due to a large array of energetically competitive spin configurations. [8][9][10][11] In particular, Cr2On clusters have been heavily studied both experimentally and theoretically, [9][10][11][12][13] showing large changes in electronic structure with oxygen content via photoelectron spectroscopy (PES), 9,12,13 and structures in agreement with vibrationally resolved IR spectroscopy. [14][15][16] The electronic structures of Cr2On clusters arise from a unique mixing of Cr half-filled s-and d-orbitals (3d 5 4s 1 ) with O 2p-orbitals.…”

“…Insights on the relaxation dynamics are provided by changes in the theoretical electronic structure of clusters with oxidation. Due to the accuracy previously demonstrated in Cr oxide clusters, 11,26 we employ density functional theory (DFT) calculations to calculate the geometries, and time-dependent DFT to determine excited states of chromium oxide clusters (Supplemental Information). In Cr2On clusters, the first two O atoms bridge between the Cr atoms, and subsequent O atoms attach to the Cr atoms while maintaining a planar geometry, in agreement with previous calculations (Figure 1).…”

“…In Cr2On clusters, the first two O atoms bridge between the Cr atoms, and subsequent O atoms attach to the Cr atoms while maintaining a planar geometry, in agreement with previous calculations (Figure 1). 10,11,27 Electronic superexchange between Cr and O atoms in Cr2On clusters (n = 1-4) makes them antiferromagnetically (AF) coupled, except for Cr2O which is ferromagnetically (FM) coupled. Although the FM state of Cr2O3 has been suggested to be degenerate, 9,10,16,27 the AF state is 0.5 eV lower in our calculations.…”

Increased Excited State Metallicity in Neutral Cr2On Clusters (n < 5) Upon Sequential Oxidation

“…Insights on the relaxation dynamics are provided by changes in the theoretical electronic structure of clusters with oxidation. Due to the accuracy previously demonstrated in Cr oxide clusters, 11,26 we employ density functional theory (DFT) calculations to calculate the geometries, and time-dependent DFT to determine excited states of chromium oxide clusters (Supplemental Information). In Cr2On clusters, the first two O atoms bridge between the Cr atoms, and subsequent O atoms attach to the Cr atoms while maintaining a planar geometry, in agreement with previous calculations (Figure 1).…”

“…In Cr2On clusters, the first two O atoms bridge between the Cr atoms, and subsequent O atoms attach to the Cr atoms while maintaining a planar geometry, in agreement with previous calculations (Figure 1). 10,11,27 Electronic superexchange between Cr and O atoms in Cr2On clusters (n = 1-4) makes them antiferromagnetically (AF) coupled, except for Cr2O which is ferromagnetically (FM) coupled. Although the FM state of Cr2O3 has been suggested to be degenerate, 9,10,16,27 the AF state is 0.5 eV lower in our calculations.…”