Truong Ba Tai, N. M. Tam, M. Nguyen
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We investigate the molecular and electronic structure and thermochemical properties of the cationic boron clusters Bn + with n = 2–20, using both MO and DFT methods. Several functionals are used along with the MP2, G3, G3B3, G4, and CCSD(T)/CBS methods. The latter is the high accuracy reference. While the TPSS, TPSSh, PW91, PB86, and PBE functionals show results comparable to high-accuracy MO methods, both BLYP and B3LYP functionals are not accurate enough for three-dimensional (3D) structures. A negligible difference is observed between the B3LYP, MP2, and CCSD(T) geometries. A transition between 2D and 3D structures occurs for this series at the B16+–B19 + sizes. While smaller clusters Bn + with n ≤ 15 are planar or quasi-planar, a structural competition takes place in the intermediate sizes of B+16–19 . The B20 ? cation has a 3D tubular shape. The standard heats of formation are determined and used to evaluate the cluster stability. The average binding energy tends to increase with increasing size toward a limit. All closed-shell species Bn+ has an aromatic character, but an enhanced stability is found for B5 + and B13 + whose aromaticity and electron delocalization are analyzed using the LOL technique.