First-principles study of AuSn (2 ≤ n ≤ 7) clusters: structural, electronic, magnetic, spectral properties, and adsorption properties with O2 and H2O

Based on the density functional theory (DFT) method, the geometrical structures, relative stability, electronic, and spectral properties of AuSn (2 ≤ n ≤ 7) clusters are systematically studied, whose sizes are largely in the range of 0.3–0.5 nm. AuS4 and AuS3 show the highest and lowest energy gaps and hence the highest chemical stability and chemical activity, respectively. The total magnetic moment is 3.0 and 1 (or 0) μB for AuS4 and other clusters, respectively, which largely (about 99.9%) arise from the local magnetic moment of S atoms. The average polarization tensor for single atom (<α¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{\alpha} $$\end{document}>) generally increases with increasing the number of S atoms, with the maximum 91.72 a.u. for AuS7, corresponding to the most significant delocalization effect. AuS4 cluster exhibits the highest polarizability anisotropic invariant Δα (≈ 350.56 a.u.) and the lowest total dipole moment (≈ 0.06 D) among all systems, corresponding to the strongest anisotropic response to external electric field and the weakest polarization, respectively. The IR, Raman, UV-Vis, and PES spectra are simulated for AuSn (2 ≤ n ≤ 7) clusters with the structures of the lowest isomers. The O–O and O–H bond lengths, adsorption energies, vibration frequencies, and density of states are also calculated for AuS4 and AuS3 adsorbing one O2 and H2O molecules, respectively. The adsorption capacity of AuS3 for both gas molecules is higher than AuS4, and AuSn (n = 3, 4) clusters are more favor to adsorb O2 than H2O.