Vibronic interactions in B4 rhomboids

Origin of rhomboid structures in B4 units were clarified for cationic, neutral, and anionic states. The molecular distortions are due to vibronic interactions of non-degenerate ground states, of which symmetries are lowered from D4h to D2h point group. Multicentered bondings with σ characters were naturally deduced from the vibronic interactions.