The most notable exception to the trend of FIT+DMA+MP2 providing the best results is for the polymorphs of adenine, where both forms have a significantly improved (i.e. lowered) ∆E value in the FIT+DMA+B3LYP model, with small improvements in ranking, compared to FIT+DMA+MP2 (Fig. ). However, estimations of relative polymorph free energies based on solubility data 50 indicate that form I is 1.1 ± 0.3 kJ/mol more stable than form II at room temperature, which is reproduced most closely by the FIT+DMA+MP2 lattice energies (Fig. ). All methods are found to overestimate the relative stability of form I, including fully optimized PBE-D3. The comparison between the experimental free energy difference and calculated lattice energy difference ignores the lattice vibrational contribution to the free energy difference between polymorphs, but this was found to be only about 0.5 The comparisons to experimental polymorph relative stability data indicate that, despite some small exceptions when using N lower and ∆E as metrics, the MP2 corrections provide the most reliable improvement to the lattice energies of force field crystal structure landscapes.