Revisiting symmetry breaking in BNB: The key role of electronic correlation

Spontaneous symmetry breaking in the ground state of the BNB molecule is revisited by employing a series of high-level multireference methods based on updated SA-CASSCF wavefunctions with larger active space. It supports our previous determination of two equivalent linear-noncentrosymmetric equilibrium configurations. The calculated magnitude of the barrier between them increases with the level of electronic correlation taken into account. The inadequate centrosymmetric structure obtained by MRCI calculations is caused by insufficient account of electronic correlation. The origin of the off-center distortion in BNB, as in many other systems, is due to the Pseudo Jahn–Teller effect.