Figure 4

Plot (a) Second derivative of the variance of the on-site number operator. The curves from top to bottom (around the maximum) correspond to M equal to 402 (black), 302 (red), and 202 (blue), respectively. Plot (b)
at the maximum. Plot (c)
at the minimum. The circles in plots (b) and (c) show QMC data, while the solid lines provide the fit (17). All plots are for kBT/U = 0.01.