Database-scale validation of Hoppe's MAPLE additivity theorem for perovskite and pyrochlore oxides

Hoppe's additivity theorem predicts that the Madelung part of lattice energy (MAPLE) of a ternary oxide should equal the weighted sum of its binary oxide components to within one percent, but it has never been tested at database scale. We present MaplePy, an open-source tool for automated MAPLE calculation from crystallographic information files, and apply it to 1,410 perovskite and pyrochlore structures from the Inorganic Crystal Structure Database. Of 1,380 testable structures, 65.9% satisfy the one-percent threshold and one in six carries a detectable problem in the electrostatic analysis. A three-tier, ten-code classification separates genuine violations of the theorem from artefacts of oxidation state assignment, disorder models and the compositional limits of the binary reference table, so that a residual is interpreted rather than merely reported. Forty-seven entries published between 2006 and 2026 carry coordinate errors severe enough that the structures are physically wrong, and none is corrected by database standardisation. Processing the same structures with bond valence analysis establishes where the two methods agree and where they do not: both flag the coordinate errors, whereas 218 perovskites satisfy bond valence analysis and fail additivity, among them the rare earth nickelates, whose systematic 1.8 to 2.8% residual is consistent with Ni–O charge-transfer covalency that bond lengths do not reveal. MaplePy and the binary oxide reference table are released as open-source tools.