FIG. 3.

The deviation (error) between binding energies calculated using various semi-empirical methods and reference values (see Table I), for the set of 15 dimers in the gas phase (gas) or solution phase (aq). The gray line denotes an estimated $\pm 1.5$ kcal/mol uncertainty in the reference values in the solution phase. The gas-phase reference of CCSD(T)/CBS is expected to carry only a small uncertainty of $\pm 0.2$ kcal/mol for which the gray error bar is not representative. See text for the discussion of the null models.