Density-functional study of the structures and properties of holmium-doped silicon clusters HoSi (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 = 3-9) are sextuplet electronic states. The structures of these Ho-doped Si clusters (aside from HoSi) are substitutional. The ground-state structures of HoSi 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 = 4-9) is only 0.04 eV. The simulated PESs for HoSi (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 HoSi and obtained an experimental AEA of 2.2 ± 0.1 eV. The dissociation energies of Ho from HoSi and HoSi (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 = 3-9) and their anions derive mainly from the Ho atom. It was also found that the magnetic moments of Ho in the HoSi clusters are larger than the magnetic moment of an isolated Ho atom.