Theoretical investigations of BBS (singlet)→BSB (triplet) transformation on a potential energy surface obtained from neural network fitting

•B2S can adopt either the B-B-S (singlet) or B-S-B (triplet) conformation.•A neural network potential energy surface for B2S transformation is developed.•The transformation pathway is predicted using the nudged elastic band method.•Molecular dynamics of the transformation is investigated with various excitations.

B2S, the simplest BnSm cluster, has been shown to exhibit an interesting ground-state structure. B3LYP/6-311G (d,p) calculations suggest that its most stable configuration is singlet linear B-B-S. When promoted to the excited triplet state, B2S adopts the B-S-B configuration (C2v point group). To characterize its structural transformation, the lowest energy at each configuration is selected, and the neural network surface is developed with symmetry exchange incorporated. The triplet potential energy is found to be 0.48 eV above the ground state. Subsequently, the nudged-elastic-band method is employed to locate the BBS→BSB transition state. It is found that the barrier height is 1.35 eV above the equilibrium singlet BBS energy (0.88 eV for the reverse reaction). In addition, quasiclassical molecular dynamics with different vibrational excitations shows that the reaction is accelerated when the bending vibrational mode of BBS is excited, while the activation of BBS stretching modes causes a negative effect.