Quantum Monte Carlo study of the electron binding energies and aromaticity of small neutral and charged boron clusters

Abstract

The valence electron binding energies and the aromaticity of neutral and charged small boron clusters with three and four atoms are investigated using a combination of the fixed-node diffusion quantum Monte Carlo (FN-DMC) method, the density functional theory, and the Hartree-Fock approximation. The obtained electron binding energies such as the adiabatic detachment energy, vertical detachment energy, adiabatic ionization potential, and the vertical ionization potential are in excellent agreement with available experimental measurements. Their decomposition into three physical components such as the electrostatic potential and exchange interaction, the relaxation energy, and the electronic correlation effects has allowed us to determine that the neutral boron clusters are stabilized by the electrostatic and exchange interactions, while the anionic ones are stabilized by the relaxation and correlation effects. The aromaticity is studied based on electronic structure principles descriptor and on the resonance energy. The FN-DMC results from the electronic structure principles of the energy, hardness, and eletrophilicity have supported the aromaticity of B− 3 , B− 4 , and B4 and partially supported the aromaticity of the clusters B3, B+ 3 , and B+ 4 . The obtained values for the resonance energy of the clusters B− 3 , B3, B+ 3 , B4, B+ 4 , and B− 4 are 55.1(7), 54.2(8), 33.9(7), 84(1), 67(1), and 58(1) kcal/mol, respectively. Therefore, the order of decreasing stability of the trimer is B− 3 > B3 > B + 3 , while for the tetramer it is B4 > B + 4 > B − 4 , which is in agreement with the results from the molecular orbital analysis.