Figure 4 - The scaled free energy density minus the ground-state energy density, (f-e0)(ħc) 2/T3, of the quantum O(N)-nonlinear 
-model in the limit N→∞ (dotted line).
From the following article
Criticality in correlated quantum matter
Angela Kopp and Sudip Chakravarty
Nature Physics 1, 53 - 56 (2005)
doi:10.1038/nphys105
In the scaling limit (T
0), this quantity approaches the asymptote -0.153
. Quantum critical scaling holds up to T*
c
/8 with 1% accuracy.