Ab Initio Study on the Potential Energy Surfaces of B₄ Cluster

Abstract

The singlet and triplet potential energy surfaces (PES) for the isomerization and dissociation reactions of B4 isomers have been investigated using ab initio methods. Ten B4 isomers have been identified and of these 10 species, 4 have not been reported previously. The singlet rhombic structure 11 is found to be the most stable on the B4 surface, in agreement with the results of previous reports. Several isomerization and dissociation pathways have been found. On the singlet PES, the linear 13b can rearrange to rhombus 11 directly, while 13c rearranges to 11 through two‐step reactions involving a cyclic intermediate. On the triplet PES, the capped triangle structure 32 undergoes ring opening to the linear isomer 33b with a barrier of 34.8 kcal/mol and 44.9 kcal/mol, and the latter undergoes ring closure to the square structure 31 with a barrier of 30.4 kcal/mol and 33.0 kcal/mol at the MP4/6–311+G(3df)//MP2/6–311G(d) and CCSD/aug‐cc‐pVTZ//MP2/6–311G(d) levels of theory, respectively. The direct decomposition of singlet B4 yielding to B3+B is shown to have a large endothermicity of 87.3 kcal/mol (CCSD), and that producing 2B2 to have activation energy of 133.4 kcal/mol (CCSD).