Ab initio search for global minimum structures of neutral and anionic B4H4 clusters

► B4H4 has a planar rather than a tetrahedral global minimum structure. ► The B4H4− anion global minimum is a distorted tetrahedral structure. ► Theoretical vertical detachment energies included here can help interpret future photoelectron spectroscopic study of the B4H4− anion. ► Bonding analysis using AdNDP reveals 4-center bonding in B4H4 and B4H4− clusters.