Structure and electronic properties of neutral and anionic boron clusters doped with two tantalum atoms

Transition metal-doped boron clusters have attracted much attention due to the novelty of electronic properties and structural evolution in recent years. In this work, we use the efficient CALYPSO structure search method to perform the globally minimum structure search for the neutral and negative Ta₂B_n(n = 1–10) clusters. Then DFT optimisation was carried out at the pbe1pbe level to obtain a lot of low-energy stable structures. Finally, the total energy was sorted to select the ground-state and low energy structure. The results show that the cluster forms a B ring when n = 6. With the number of B atoms increases, the B ring with the line of two Ta atoms as the axis becomes larger and larger. Neutral Ta₂B₆ clusters with bipyramid structure and protruding stability were found by relative stability analysis, the HOMO–LUMO gap was 2.75 eV. The chemical bonds of closed-shell D_6h Ta₂B₆ were analysed by using the adaptive natural density partitioning (AdNDP) method. It was found that the interaction between the B₆ ring and the apex Ta atom is carried out by six 4c-2e π bonds. In addition, bonding analysis shows that the strong d-p interaction between tantalum and boron atomic orbitals can effectively improve the stability of Ta₂B₆ clusters.