Competition between structural distortion and magnetic moment formation in fullerene C20.

We investigate the effect of on-site Coulomb interactions on the structural and magnetic ground state of C(20) fullerene based on density-functional-theory calculations within the local density approximation (LDA) plus on-site Coulomb corrections (LDA+U). The total energies of the high symmetry (I(h)) and the distorted (D(3d)) structures of C(20) are calculated for different spin configurations. The ground state configurations are found to depend on the forms of exchange-correlation potentials and the on-site Coulomb interaction parameter U, reflecting the subtle nature of the competition between Jahn-Teller distortion and magnetic instability in the C(20) fullerene. While the nonmagnetic state of the distorted D(3d) structure is robust for small U, a magnetic ground state of the undistorted I(h) structure emerges for U larger than 4 eV when the LDA exchange-correlation potential is employed.