Transition from exohedral to endohedral geometries of anionic and neutral B4Sin (n = 4–15) clusters: quantum chemical calculations

Abstract

The growth patterns of anionic and neutral B₄Si_n (n = 4–15) clusters are investigated by using density functional theory (DFT) calculations combined with particle swarm optimization (CALYPSO) software. The geometries of anionic and neutral B₄Si_n clusters transform from exohedral to endohedral structures with the increasing cluster sizes. The B₄Si₁₄⁻ anion size is critical for forming B₄-endohedral structures for anionic clusters, while the B₄Si₁₅ neutral size is the threshold size for forming B₄-endohedral structures for neutral clusters. Both anionic and neutral B₄Si_n (n = 4–15) clusters are primarily dominated by prism-based or bipyramid-based geometries. The global minima of anionic and neutral B₄Si_n clusters adopt different geometrical structures, except for anionic and neutral B₄Si₁₀. The binding energies, second-order energy differences, and incremental binding energies of B₄Si_n⁻ clusters show an odd–even alternation with the growing number of Si atoms. The B atoms in B₄Si_n^−/0 exhibit B–B single bonding and BB double bonding properties. The B atoms are found to carry more negative charges due to charge transfer from Si_n frameworks to B atoms. Interestingly, the B₄Si₄⁻ anion adopts a C_2h symmetric bicapped tetragonal bipyramid with σ plus π double bonding characters and has the highest relative stability among the anionic clusters. The bonding interactions in B₄Si₄⁻ are in the order of B–B > B–Si > Si–Si.