Systematic research on gallium atom-doped neutral small- and medium-sized gas-phase magnesium clusters: A DFT study of GaMg_n (n=2–12) clusters

Structure, stability, charge transfer, chemical bonding, and spectroscopic properties of Ga atom-doped neutral Mg_n (n = 2–12) clusters have been systematically investigated by CALYPSO and density functional theory. All cluster structures are based on “tetrahedral” and “yurt-like” growth except for GaMg₂. The ground state isomer of GaMg₈ with high symmetry structure is predicted to be the best-fit candidate for the “magic” cluster because of its excellent stability. Natural bond orbital calculations reveal that Ga and Mg atoms play the role of electron acceptor and donor in all ground state isomers, while the orbitals in both Ga and Mg are sp-hybridized. Most importantly, chemical bonding studies based on atom-in-molecular theory have shown that the lowest-energy state of GaMg₄ is so special, in that it has not only the critical size for the appearance of Mg–Mg covalent bonds, but also the only cluster that has both Ga–Mg covalent and non-covalent bonds. Finally, theoretical calculations of IR and Raman spectra of all ground state isomers indicate that the spectra of these clusters are observable in the low-frequency band, and thus they can be identified by spectroscopic experiments. Furthermore, the bond heterogeneity of the Ga–Mg in the GaMg₄ ground state isomer has also been specifically investigated, including the fixed GaMg₄ structure with Mg atoms added in different directions, as well as ab initio molecular dynamics sampling at different temperatures.