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

A systematic investigation of the boron-doped silicon clusters SinB 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 SinB with n = 1-10 emerges as follows: (i) each SinB cluster is formed by adding one excess Si-atom into the smaller sized SinB, rather than by adding B into Si-n, (ii) a competition between the exposed (exohedral) and enclosed (endohedral) structures occurs at the size Si8B where both structures become close in energy, and (iii) the larger size clusters Si9B and Si10B exhibit endohedral structures where the B-impurity is located at the center of the corresponding Si-n cages. The species Si9B-, Si9B, and Si10B+ are identified as enhanced stability systems with larger average binding energies and embedded energies. The higher stability of the closed shells Si9B- and Si10B+ can be rationalized in terms of the jellium electron shell model and spherical aromaticity.