Chemprop Model

A Message Passing Neural Network (MPNN) surrogate model using ``Chemprop v2.x <https://chemprop.readthedocs.io/>``_ as the backbone. Accepts SMILES strings as inputs and returns scalar fitness predictions.

The model uses bond-based message passing (BondMessagePassing), a configurable graph-level aggregation function, and a feed-forward regression head (RegressionFFN). The network is initialised lazily on the first train() call; subsequent calls fine-tune from the current weights rather than resetting them.

Key properties:

• Input: SMILES strings stored in Candidate.data

• Output: Mean-only scalar predictions (no uncertainty estimates)

• Aggregation: mean (default), sum, or norm

• Sampling: Not supported — raises NotImplementedError

Note

This model requires the optional chemprop dependency. Install it with the [chemprop] extra:

pip install "alf-tools[chemprop]"