Bond stretch isomerism in Be₃^2- driven by the Renner-Teller effect

We investigate the underlying principle behind the occurrence of bond stretch isomerism in Be₃^2-, which has not been revealed yet. Various computational studies of the different isomers are carried out at the complete active space self-consistent field (CASSCF) level of theory in addition to the B3LYP level in conjunction with the 6-311++G(d) basis set. The potential energy surfaces linking the different isomers through transition states and conical intersections are investigated at the CASSCF level, connecting various geometrical isomers of Be₃^2-. The linear intermediate of the Be₃^2- cluster is considered to be of profound importance since its excited state is found to be degenerate and undergoing the Renner-Teller effect, producing two triangular bond stretch isomers. Ab initio molecular dynamics simulations based on the Atom Centered Density Matrix Propagation (ADMP) method also further elucidate the phenomenon of isomerization via the linear intermediate. The variation of the global reactivity descriptors and free energy profile along the bond stretch isomerization path is also investigated. The estimated aromatic stabilization energy also corroborates the stability ordering of the bond stretch isomers.