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Abstract

This paper investigates the Jahn–Teller effect in the icosahedral cation B₈₀⁺ and compares the descent in symmetry with that in C₆₀⁺. For both cations the icosahedral ground state is a ²H_u state, which exhibits a H [multiply sign in circle] (g ⊕ 2h) Jahn–Teller instability. A detailed construction of the potential energy surface of B₈₀⁺ using different DFT methods including B3LYP/6-31G(d), VWN/6-31G(d), PBE/TZP and PBE/6-31G(d) shows that, contrary to C₆₀⁺, which prefers D_5d symmetry, the ground state of B₈₀⁺ adopts S₆ point group symmetry. A D_3d structure is identified as a saddle point among the S₆ minima of B₈₀⁺. The distortion of D_3d to S₆ in B₈₀⁺ is attributed to a superposition of Jahn–Teller and pseudo-Jahn–Teller effects. Imaginary modes, transforming as the g_g representation, which are present in neutral icosahedral B₈₀, form the dominant symmetry breaking active modes. The pronounced difference between the JT effects in the boron and carbon buckyball cations is due to the plasticity of the boron caps. The calculated Jahn–Teller stabilization of B₈₀⁺ is nearly 1549 cm⁻¹ (PBE/TZP), which exceeds the stabilization of 596 cm⁻¹ computed for C₆₀⁺ at the same level.