s |∇ρ|) at a given point in space. Data is weighted by the LDA exchange energy density (∝ ρ 4/3 ) so that the heat map approximates the relative importance of different values of f 1 and f 2 to the xc energy. Put another way, it represents the likelihood that errors in the DFA at those values will contribute substantially to errors in the xc energy for the system. We focus on features from DM21: the density gradient, |∇ρ(⃗ r)|, kinetic energy density, τ