Structural evolution, charge transfer and bonding properties of medium-sized atomic rubidium-doped boron clusters

Abstract

In this work, particle swarm optimization (CALYPSO) is combined with density functional theory (DFT) to perform a comprehensive structure search for the B_n^0/−Rb₂ (n = 1–12) clusters. The ground-state structures of the B_n^0/−Rb₂ (n = 1–12) clusters were determined based on the total energy of the obtained structures. It was also found that when the number of B atoms was low, the doped cluster geometry mainly behaved as planar or planar-like. The addition of doped Rb atoms distorts the boron clusters, with the doping position around the main body of boron. The stability analysis shows that the B₈Rb₂ cluster with a double pyramidal structure and a symmetry of D_7h has excellent stability in the studied system. The energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital is 6.14 eV. Bonding analysis is performed using molecular orbitals and density of states, and the results show that strong communications between the two Rb atoms and the B-atom bulk dominate their significant stability, where mainly the p atom orbital of the Rb atoms interacts with the s and p atom orbitals of the B atoms. Furthermore, the bond level density and naturally adapted orbital analysis revealed that the formation of effective π-type naturally adapted orbitals between the doped Rb atoms and the B atoms, with a higher delocalization index, is one of the reasons for the higher cluster stability.