Unveiling the structural evolution and electronic properties of sodium–aluminum alloy clusters

This study systematically investigates the geometric structures and electronic properties of Na_nAl_n^−/0 (n = 2 − 10) clusters using a hybrid global optimization algorithm and density functional theory calculations. The ground-state structures of anionic Na_nAl_n⁻ (n = 2–6) were determined by comparing theoretical and experimental photoelectron spectra. The results indicate structural consistency between neutral and anionic clusters for most sizes, except n = 4 and 9. Al atoms tend to form the cluster core while maintaining geometries isomorphic to their free-standing configurations for n = 2–4, whereas Na atoms preferentially occupy surface sites. In all clusters, Na acts as an electron donor and Al as an electron acceptor. Neutral Na₅Al₅ and its analogs AM₅Al₅ (AM = Li, K, Rb, Cs) are identified as superatoms with a distinctive 1S²1P⁶2S²1D¹⁰ electron configuration and exhibit significant aromatic character.