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In this study, the unbiased crystal structure analysis by particle swarm optimisation (CALYPSO) combined with the density functional theory (DFT) method were used to perform a structure search for neutral Cs2Bn (n = 1–12) clusters, as well as the corresponding global minimum of the potential energy surface were determined. The ground-state structures of the Cs2Bn (n = 1–12) clusters have four types of geometries: planar, arch bridge, double pyramid, and shield shape. Subsequently, the relative stability of the ground-state structures was systematically analysed based on three effective rules, which indicates that the C7V Cs2B8 with a double pyramid structure has unusual stability. The results of the molecular orbitals (MOs) and density of states analysis (DOS) show that the B-2s and 2p atomic orbitals of Cs2B8 are the main components of MOs. In addition, from the results of adaptive natural density partitioning (AdNDP) and localised orbital locator (LOL), it can be seen that the excellent stability of Cs2B8 originates from the delocalised large π bonds with aromaticity and the s–p bonding of B–B. Our results reveal the structural growth mode of Cs2Bn clusters and enrich the chemical bonding properties of boron-based clusters. [ABSTRACT FROM AUTHOR]

To understand the effects of Cs on pure boron clusters, the growth mode, electronic properties, and bonding characteristics of CsB n 0/− (n = 2–12) clusters were discussed by CALYPSO combined with DFT method. Photoelectron spectra of the ground-state structures are reliable and efficient based on the accurate structure search method, which can provide theoretical information for future related studies. Through the study of the three valid criteria, we conclude that the CsB 8 and CsB 8 − with point group symmetry C 7V have outstanding stability and electronic properties. The orbital composition analysis indicates that the molecular orbitals of these two clusters are mainly composed of B-2 s and B-2 p atomic orbitals (AOs), and there is a strong interaction between these two AOs. Furthermore, we also found that the high stability of CsB 8 and CsB 8 − clusters mainly originates from the s - p bonding, σ and π bonds of B–B, especially the CsB 8 − cluster has (σ+π) double aromaticity. • The evolution of the structures for CsB n (n = 2-12) clusters has be elucidated. • The corresponding ground state structures are determined. • It is found that the most stable isomer is a double pyramid structure with double aromaticity. • The molecular orbitals and bonding characteristics of the most stable structure are discussed by various methods. [ABSTRACT FROM AUTHOR]