Pseudo-Jahn–Teller origin of icosahedral instability in boron buckyball, B80

A study of Ih to Th pseudo-Jahn–Teller (PJT) distortion in B80 is presented. Reduced matrix elements for vibronic coupling and resulting force constants were calculated in Ih to elucidate the origin of B80 symmetry breaking. Important orbital excitations involved are between inner orbitals 9hg, 5hg, and 6gu and virtual orbitals 8t2u and 8gg. Low-lying occupied orbitals interact more strongly than frontier molecular orbitals due to their density distribution on the capping atoms. The large energy gaps, associated with these excitations, attenuate the PJT effect. The force constant calculations for B80 point to a weak PJT energy stabilization of 304 cm−1 at B3LYP/6-31G(d).