Figure 4
From: Exact exchange-correlation potential of an ionic Hubbard model with a free surface
Contributions to the charge gap in the different regimes.
Panel (a) and (b) show the different contributions to the gap, ΔKS and Δxc and compare their sum to the exact charge gap calculated by Lanczos diagonalization, ΔC. The parameters in the two panels are chosen to have the same total charge gap at U = 0 in the small hopping limit. Parameters are in panel (a) δ = 2t, V = 0, in panel (b) δ = t, V = 0.5t. In both panels we set w0 = −6t + U/2 and the potential of the site closer to the bulk-vacuum boundary has been shifted to minimize boundary effects.
