Electronic Structures and Thermochemical Properties of the Small Silicon‐Doped Boron Clusters B n Si ( n =1–7) and Their Anions

We perform a systematic investigation on small silicon‐doped boron clusters B n Si ( n =1–7) in both neutral and anionic states using density functional (DFT) and coupled‐cluster (CCSD(T)) theories. The global minima of these B n Si 0/− clusters are characterized together with their growth mechanisms. The planar structures are dominant for small B n Si clusters with n ≤5. The B 6 Si molecule represents a geometrical transition with a quasi‐planar geometry, and the first 3D global minimum is found for the B 7 Si cluster. The small neutral B n Si clusters can be formed by substituting the single boron atom of B n +1 by silicon. The Si atom prefers the external position of the skeleton and tends to form bonds with its two neighboring B atoms. The larger B 7 Si cluster is constructed by doping Si‐atoms on the symmetry axis of the B n host, which leads to the bonding of the silicon to the ring boron atoms through a number of hyper‐coordination. Calculations of the thermochemical properties of B n Si 0/− clusters, such as binding energies (BE), heats of formation at 0 K (ΔH f 0 ) and 298 K (ΔH f [ 298] ), adiabatic (ADE) and vertical (VDE) detachment energies, and dissociation energies ( D e ), are performed using the high accuracy G4 and complete basis‐set extrapolation (CCSD(T)/CBS) approaches. The differences of heats of formation (at 0 K) between the G4 and CBS approaches for the B n Si clusters vary in the range of 0.0–4.6 kcal mol −1 . The largest difference between two approaches for ADE values is 0.15 eV. Our theoretical predictions also indicate that the species B 2 Si, B 4 Si, B 3 Si − and B 7 Si − are systems with enhanced stability, exhibiting each a double (σ and π) aromaticity. B 5 Si − and B 6 Si are doubly antiaromatic (σ and π) with lower stability.