Thermochemical Parameters and Growth Mechanism of the Boron-Doped Silicon Clusters, Si_nB^q with n = 1–10 and q = −1, 0, +1

A systematic investigation of the boron-doped silicon clusters Si n B with n ranging from 1 to 10 in the neutral, anionic, and cationic states is performed using quantum chemical calculations. Lowest-energy minima of the clusters considered are identified on the basis of the B3LYP, G4, and CCSD(T) energies. Total atomization energies and thermochemical properties such as ionization energy, electron affinity, and dissociation energies are obtained using the high accuracy G4 (B3LYP-MP4-CCSD(T)) and CCSD(T)/CBS (complete basis set up to n = 4) methods. Theoretical heats of formation are close to each other and used to assess the available experimental values. The growth mechanism for boron-doped silicon clusters Si n B with n = 1–10 emerges as follows: (i) each Si n B cluster is formed by adding one excess Si-atom into the smaller sized Si n –1 B, rather than by adding B into Si n, (ii) a competition between the exposed (exohedral) and enclosed (endohedral) structures occurs at the size Si 8 B where both structures become close in energy, and (iii) the larger size clusters Si 9 B and Si 10 B exhibit endohedral structures where the B-impurity is located at the center of the corresponding Si n cages. The species Si 9 B –, Si 9 B, and Si 10 B + are identified as enhanced stability systems with larger average binding energies and embedded energies. The higher stability of the closed shells Si 9 B – and Si 10 B + can be rationalized in terms of the jellium electron shell model and spherical aromaticity.