Competition between structural distortion and magnetic moment formation in fullerene C$_{20}$

TL;DR

This study explores how Coulomb interactions influence the structural and magnetic states of fullerene C20, revealing a delicate balance between distortion and magnetism depending on interaction strength and computational approach.

Contribution

It demonstrates the dependence of C20's ground state on Coulomb interactions and exchange-correlation potentials, highlighting the competition between Jahn-Teller distortion and magnetic instability.

Findings

Non-magnetic distorted D3d structure is stable at small U.

Magnetic undistorted Ih structure appears at U > 4 eV with LDA.

Ground state configuration varies with U and exchange-correlation choice.

Abstract

We investigated the effect of on-site Coulomb interactions on the structural and magnetic ground state of the fullerene C$_{20}$ based on density-functional-theory calculations within the local density approximation plus on-site Coulomb corrections (LDA+$U$). The total energies of the high symmetry ($I_{h}$) and distorted ($D_{3d}$) structures of C$_{20}$ were calculated for different spin configurations. The ground state configurations were 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 fullerene C$_{20}$. While the non-magnetic 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.