In Figure (b), we decompose GEO s into the contributions from C-H and C ----C bonds, and angles. These results for the phenyl radical can also be compared with those for the benzene molecule [Figure ]. From this plot, we can see that large GEO of MP2 comes almost exclusively from the errors in the C ----C bond lengths. Instead of summing contributions for the same bond types, we can also measure the GEO contributions from each bond. While a more detailed analysis is shown in the SI (Fig. ), we focus on MP2 in Figure , where for each unique bond length we show errors in pm. We can also see how each of these translate to GEO contributions, which are obtained by squaring the error and multiplying it by half of the underlying force constant (Eq. 9). We can see that the MP2 errors in C ----C bond lengths are very large and range from ∼2.5pm to ∼3pm resulting in GEO contributions from 0.3 to 0.5 kcal/mol per bond. The errors in the C-H bond lengths are much smaller, and result in way smaller GEO s contributions given that: GEO grows quadratically with the errors in geometric parameters and given the smaller value of the f C-H than f C ----C force constant. In contrast to the large MP2 errors in C ----C bonds, those of B2PLYP are much smaller (within 0.16 pm resulting in negligible GEO contributions, ∼0.001 kcal/mol).