Estimates of effective Hubbard model parameters for C20 isomers

We report on an effective Hubbard Hamiltonian approach for the study of electronic correlations in C20 isomers—cage, bowl, and ring—with quantum Monte Carlo and exact diagonalization methods. The tight-binding hopping parameter, t, in the effective Hamiltonian is determined by a fit to density-functional theory calculations, and the on-site Coulomb interaction, U/t, is determined by calculating the isomers’ affinity energies, which are compared …