Determination of the ground state structures of anionic Gan (n = 2–15) clusters

The global minimum structures and electronic properties of anionic and neutral Ga_n^−/0 (n = 2–15) clusters were studied through a hybrid particle swarm optimization and genetic algorithm in combination with density functional theory (DFT) calculations. The correctness of the structures of Ga_n⁻ (n = 2–15) has been determined through the comparison of experimental and simulated photoelectron spectra (PESs). Both of anionic and neutral states share the same geometric configurations, which are similar to those of the In_n clusters, but different from Al_n clusters. It is found that the Ga clusters gradually grow to a distorted cubic structure from n = 2–8, and then form an elongated pentagonal bipyramid at n = 13. By adding an extra Ga atom to one of the square faces of Ga₁₃ can obtain the structure of Ga₁₄, while Ga₁₅ takes a completely different prolate structure. Among these anionic and neutral clusters, Ga₁₃⁻ cluster possesses the largest vertical detachment energy, adiabatic detachment energy, HOMO-LUMO gap, average binding energies, and second order energy difference values, which can be attributed to its being a superatom with the electronic configuration of (1S)²(1P)⁶(1D)¹⁰(2S)²(1F)¹⁴(2P)⁶. The constructed alkali-halide AMGa₁₃ (AM = Li, Na, K, Rb, Cs) clusters also exhibit superatomic characteristics with the same electronic configuration as that of Ga₁₃⁻.