Using metatensor models for dataset exploration

In this example, we demonstrate how to create and use a metatensor model with chemiscope.metatensor_featurizer() to extract features from the model, which are then displayed using a chemiscope widget. To use this function, some additional dependencies are required. You can install them with the following command:

pip install chemiscope[metatensor]

Firstly, we import necessary packages and read structures from the dataset.

from typing import Dict, List, Optional

import ase.io
import torch
from metatensor.torch import Labels, TensorBlock, TensorMap
from metatensor.torch.atomistic import (
    MetatensorAtomisticModel,
    ModelCapabilities,
    ModelMetadata,
    ModelOutput,
    NeighborListOptions,
    System,
)

import chemiscope

frames = ase.io.read("data/explore_c-gap-20u.xyz", ":")

Using pre-trained models

Most commonly, you will have an already existing model in metatensor format that you’ll want to use for dataset exploration. In this case, you’ll have to create a featurizer function using chemiscope.metatensor_featurizer().

metatensor_featurizer takes an existing model as input. It can be either a MetatensorAtomisticModel instance or a path to a pre-trained model file (here "model.pt")

featurizer = chemiscope.metatensor_featurizer(model="model.pt")

From here, you can use chemiscope.explore() to visualize the features computed from the structures. For this, we are passing the frames, the featurizer function, and — as the model computes per-atom properties — environments.

chemiscope.explore(
    frames=frames,
    featurize=featurizer,
    environments=chemiscope.all_atomic_environments(frames),
)

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Defining a custom model

Let’s now move on and see how one can define a fully custom model to use through the metatensor interface.

Here we will use an atom-centered representation, where each atomic environment is represented with the moments of the positions of the neighbors up to a maximal order.

The model computes moments up to a specified maximum order \(k_{\text{max}}\), computing a representation \(F_i^k\)

\[F_i^k = \sum_{j} \frac{r_{ij}}{r_c}^k\]

where \(r_{ij}\) is the distance between atom \(i\) and its neighbor \(j\), \(k\) is the moment order and \(r_c\) is the cutoff radius.

And then, the model will take a PCA of the above features to extract the three most relevant dimensions.

class FeatureModel(torch.nn.Module):
    def __init__(self, cutoff: float, max_k: int):
        super().__init__()
        self.cutoff = cutoff
        self.max_k = max_k

        self._neighbors_options = NeighborListOptions(cutoff=cutoff, full_list=True)

    def requested_neighbor_lists(self) -> List[NeighborListOptions]:
        # our model requires a neighbor list, that will be computed and provided to it
        # automatically.
        return [self._neighbors_options]

    def forward(
        self,
        systems: List[System],
        outputs: Dict[str, ModelOutput],
        selected_atoms: Optional[Labels] = None,
    ) -> Dict[str, TensorMap]:
        if list(outputs.keys()) != ["features"]:
            raise ValueError(
                "this model can only compute 'features', but outputs contains other "
                f"keys: {', '.join(outputs.keys())}"
            )

        if not outputs["features"].per_atom:
            raise NotImplementedError("per structure features are not implemented")

        all_features = []
        all_samples = []

        for system_i, system in enumerate(systems):
            dtype = system.positions.dtype
            device = system.positions.device
            n_atoms = len(system.positions)

            # Initialize a tensor to store features for each atom
            features = torch.zeros((n_atoms, self.max_k), dtype=dtype, device=device)

            # get the neighbor list for this system
            neighbors = system.get_neighbor_list(self._neighbors_options)
            i = neighbors.samples.column("first_atom")

            r_ij = torch.linalg.vector_norm(neighbors.values.reshape(-1, 3), dim=1)
            r_ij /= self.cutoff

            for k in range(self.max_k):
                features[i, k] += torch.pow(r_ij, k)

            all_features.append(features)

            # Create labels for each atom in the system
            system_atom_labels = torch.tensor(
                [[system_i, atom_i] for atom_i in range(n_atoms)]
            )
            all_samples.append(system_atom_labels)

        # Concatenate features and labels across all systems
        features_tensor = torch.cat(all_features, dim=0)
        samples_tensor = torch.cat(all_samples, dim=0)

        # Take the PCA of the features
        _, _, V = torch.linalg.svd(features_tensor - features_tensor.mean())
        features_pca = features_tensor @ V[:3].T

        # Add metadata to the output
        block = TensorBlock(
            values=features_pca,
            samples=Labels(names=["system", "atom"], values=samples_tensor),
            components=[],
            properties=Labels(
                names=["feature"],
                values=torch.tensor([[0], [1], [2]]),
            ),
        )
        return {
            "features": TensorMap(
                keys=Labels(names=["_"], values=torch.tensor([[0]])), blocks=[block]
            )
        }

With the class defined, we can now create an instance of the model, giving cutoff and max_k as a maximal moment to compute. We don’t need to train this model since there are no trainable parameters inside.

model = FeatureModel(cutoff=4.5, max_k=6)

Next, we set up the model metadata and capabilities:

metadata = ModelMetadata(
    name="Example moment model",
    description=(
        "A model that computes atom-centered features based on the distances of "
        "neighboring atoms"
    ),
)

capabilities = ModelCapabilities(
    outputs={
        "features": ModelOutput(per_atom=True),
    },
    atomic_types=[6],
    interaction_range=0.0,
    supported_devices=["cpu"],
    dtype="float64",
)

model = MetatensorAtomisticModel(model.eval(), metadata, capabilities)

For a more detailed example of exporting a model, please check the related documentation page in metatensor.

Once the model is fully defined, we can use it with chemiscope.metatensor_featurizer():

featurizer = chemiscope.metatensor_featurizer(model, check_consistency=True)
chemiscope.explore(
    frames=frames,
    featurize=featurizer,
    environments=chemiscope.all_atomic_environments(frames),
)

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