  Matbench Discovery simulates the deployment of machine learning (ML) energy
models in a high-throughput search for stable inorganic crystals. We address
the disconnect between (i) thermodynamic stability and formation energy and
(ii) in-domain vs out-of-distribution performance. Alongside this paper, we
publish a Python package to aid with future model submissions and a growing
online leaderboard with further insights into trade-offs between various
performance metrics. To answer the question which ML methodology performs best
at materials discovery, our initial release explores a variety of models
including random forests, graph neural networks (GNN), one-shot predictors,
iterative Bayesian optimizers and universal interatomic potentials (UIP).
Ranked best-to-worst by their test set F1 score on thermodynamic stability
prediction, we find CHGNet > M3GNet > MACE > ALIGNN > MEGNet > CGCNN > CGCNN+P
> Wrenformer > BOWSR > Voronoi tessellation fingerprints with random forest.
The top 3 models are UIPs, the winning methodology for ML-guided materials
discovery, achieving F1 scores of ~0.6 for crystal stability classification and
discovery acceleration factors (DAF) of up to 5x on the first 10k most stable
predictions compared to dummy selection from our test set. We also highlight a
sharp disconnect between commonly used global regression metrics and more
task-relevant classification metrics. Accurate regressors are susceptible to
unexpectedly high false-positive rates if those accurate predictions lie close
to the decision boundary at 0 eV/atom above the convex hull where most
materials are. Our results highlight the need to focus on classification
metrics that actually correlate with improved stability hit rate.
