We considered distance-based models ranging from d = 2.5 Å to d = 10.0 Å but only the 4 Å and 6 Å models are listed in Table , as these were judged to provide reasonable accuracy while also affording models that are comparable in size to those obtained in other ways. As we saw with the τ 2B models in Section 3 .2, increasing d (to increase model size) improves the MBE(2) and MBE(3) accuracy only up to a point; errors eventually reach a plateau such that larger models do not improve the results, as compared to a value of ∆E int computed without fragmentation. For some systems, that plateau is reached at d = 5 Å while for others the fragmentation errors continue to decrease until the model reaches d = 8 Å. Errors for models ranging from 2.5-10.0 Å can be found in Tables .