Density-functional study of the structures and properties of holmium-doped silicon clusters HoSi n (n = 3-9) and their anions.

The structures and properties of Ho-doped Si clusters, including their adiabatic electron affinities (AEAs), simulated photoelectron spectra (PESs), stabilities, magnetic moments, and charge-transfer characteristics, were systematically investigated using four density-functional methods. The results show that the double-hybrid functional (which includes an MP2 correlation component) can accurately predict the ground-state structure and properties of Ho-doped Si clusters. The ground-state structures of HoSi n (n = 3-9) are sextuplet electronic states. The structures of these Ho-doped Si clusters (aside from HoSi7) are substitutional. The ground-state structures of HoSi n- are quintuplet electronic states. Their predicted AEAs are in excellent agreement with the experimental ones. The mean absolute error in the theoretical AEAs of HoSi n (n = 4-9) is only 0.04 eV. The simulated PESs for HoSi n- (n = 5-9) are in good agreement with the experimental PESs. Based on its simulated PES and theoretical AEA, we reassigned the experimental PES of HoSi4- and obtained an experimental AEA of 2.2 ± 0.1 eV. The dissociation energies of Ho from HoSi n and HoSi n- (n = 3-9) were evaluated to test the relative stabilities of the clusters. HOMO-LUMO gap analysis indicated that doping the Si clusters with the rare-earth metal atom significantly increases their photochemical reactivity. Natural population analysis showed that the magnetic moments of HoSi n (n = 3-9) and their anions derive mainly from the Ho atom. It was also found that the magnetic moments of Ho in the HoSi n clusters are larger than the magnetic moment of an isolated Ho atom.