We have performed ab initio molecular orbital calculations on the clusters modeling the medium-range ordering (MRO) region of B2O3 glass at the Hartree-Fock (HF)/6-31G* levels. Their equilibrium geometries, harmonic vibrational frequencies, and Raman scattering intensities have been calculated. The calculations have reproduced the boson peak frequencies of vitreous B2O3 observed at 24 cm-1 and 137 cm-1. The normal coordinates have demonstrated that these low-frequency vibrational modes are due to the wavelike motions of atoms within the region composed of one (for the mode at 137 cm-1) or two (for the mode at 24 cm-1) boroxol ring(s). The results suggest that the boson peak originates from the collective harmonic vibrations localized in the MRO region of glasses
