Calculating the equilibrium structure of the BNB molecule: Real s. artifactual symmetry breaking
Approximate electronic structure calculations on the ground state of the BNB molecule are subject to artifactual symmetry breaking as well as a potential second-order Jahn–Teller distortion along its antisymmetric stretch coordinate. In addition, the bending mode is very floppy and has a large anharmonic coupling with the symmetric stretch. Hence, this molecule presents a major challenge for theoretical electronic structure methods. We present a series of calculations designed to distinguish the real from the artifactual symmetry breaking. Our results give the minimum structure as C∞v, with the D∞h transition state 161 ± 20 cm−1 higher in energy, thus lying below the first vibrational level.