Eur. Phys. J. B 35, 57-68 (2003)
https://doi.org/10.1140/epjb/e2003-00256-6

Hund's rule magnetism in C₆₀ ions?

¹ International School for Advanced Studies (SISSA), Via Beirut 4, 34014 Trieste, Italy
² INFM Democritos National Simulation Center, and INFM, Unità Trieste, Italy
³ Daresbury Laboratory, Warrington WA4 4AD, UK
⁴ Dip. Fisica, Università di Milano, Via Celoria 16, 20133 Milano, Italy
⁵ INFM, Unità di Milano, Milano, Italy
⁶ International Centre for Theoretical Physics (ICTP), PO Box 586, 34014 Trieste, Italy

Corresponding author: ^a nicola.manini@mi.infm.it

Received: 17 April 2003
Published online: 22 September 2003

Abstract

We investigate the occurrence of Hund's rule magnetism in C molecular ions, by computing the ground-state spin for all charge states n from -3 to +5. The two competing interactions, electron-vibration (e-v, including Jahn Teller, favoring low spin) and electron-electron (e-e, including Hund-rule exchange, favoring high spin), are accounted for based on previously computed ab initio coupling parameters. Treating the ion coordinates as classical, we first calculate and classify the static Jahn-Teller distorted states for all n, inclusive of both e-v and e-e effects. We then correct the adiabatic result by including the zero-point energy lowering associated with softening of vibrations at the adiabatic Jahn-Teller minima. Our overall result is that while, like in previous investigations, low-spin states prevail in negative ions, Hund's rule high spin dominates all positive C ions. This suggests also that Hund-rule magnetism could arise in fullerene cation-based solid state compounds, particularly those involving C.