TM₄B₁₈ ^0/- (TM = Hf, Ta, W, Re, Os): new structure construction with TM doped B wheel units

We report the global search for the lowest energy structures of the transition metal (TM) doped B clusters, TM₄B₁₈ ^0/- (TM = Hf, Ta, W, Re, Os) and their electronic properties. A combination of the comprehensive genetic algorithm (CGA) method with density functional theory (DFT) calculations shows that they are composed of four planar TM@B₉ wheel units by sharing B atoms, except for Os₄B₁₈ ^0/-, which consists of two types of planar molecular wheels of Os@B₇ and Os@B₈. Among these nanoclusters, it is found that the Ta₄B₁₈ cluster has a closed-shell with a large HOMO-LUMO gap of 2.61 eV. Adaptive natural density partitioning analysis (AdNDP) reveals that the Ta₄B₁₈ cluster has σ antiaromaticity and π aromaticity, i.e., a conflicting aromaticity. The simulated photoelectron spectra (PES) of all anionic clusters are also provided for future experimental investigations.