Schweidtmann et al. compared the performance of such aggregation functions for different datasets. The optional additional molecular features, x m , may be provided features from outside sources (SI Section S1.2) or generated engineered fingerprints (Morgan circular fingerprints and RDKIT 2D fingerprints are implemented in Chemprop). By default, x m is empty such that the molecular embedding is simply an aggregation over atomic embeddings, i.e. h m = h ′ m . In summary, Module 3 produces molecular embeddings h m of length h plus the size of x m . Chemprop offers the option to circumvent Modules 1-3 and only using x m as fixed molecular embedding, so that h m = x m .