Same 2.4 eV band gap, different routes: SHAP explains per-prediction feature contributions

bravo_abad · x · 2026-11-01

An explainability explainer for materials-science ML: a model can predict the same 2.4 eV band gap for two crystals for very different reasons.

SHAP (SHapley Additive exPlanations) starts from a reference prediction (usually the model's average over a background dataset) and assigns each descriptor an eV contribution that sums exactly to the final prediction. In the example with a 1.6 eV reference, material A is pushed up by electronegativity (+0.9) and d-band width (+0.5), while material B is pushed up by coordination (+0.8) and cell volume (+0.6) — same 2.4 eV, different decomposition.

Global feature-importance rankings can't reveal this per-prediction difference; the accompanying chart visualizes both waterfall decompositions.

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