PhysDFTBench: Which Exact Conditions Survive from Architecture to Released Neural Exchange–Correlation Functionals?

Whether released neural functionals inherit the exact conditions hand-built functionals secure by construction is an empirical question. We find no third-party audit of these releases: commonly cited audits evaluate no neural network. PhysDFTBench audits seven exact-condition families under declared protocols and a sealed coverage rule. It reads PBE, DM21's four released weights, Skala-1.1, three controls, our own correction and pcNN in part. Deployed identities fail in released weights. DM21 breaks spin permutation and the uniform-gas limit, and the fractional-charge tail and midpoint readings order the columns differently. For the conditions no deployed construction guarantees, which ones survive is a property of the trained weights, not of the architecture. DM21's supplementary material describes strict and approximate spin-symmetrisation routes. We test the released implementation: a reference-free test puts all four released DM21 weights outside their own round-off in the deployed energy, by 0.02–2.2 mHa. A 5,123-parameter neural correction is our controlled testbed. A loss term written directly on a criterion quantity need not reach that criterion even on its own probe. We also give a three-class rule for omitting the SCF response. In the unprotected class the omitted term need not vanish, and in our own loss it did not.