Fixing model loading logic (names and cache dir) for fairchem models

tests/models/test_fairchem.py

@@ -10,6 +10,9 @@
     from collections.abc import Callable
 
     from ase.build import bulk, fcc100, molecule
+    from fairchem.core.calculate.pretrained_mlip import (
+        pretrained_checkpoint_path_from_name,
+    )
     from huggingface_hub.utils._auth import get_token
 
     import torch_sim as ts
@@ -222,6 +225,28 @@ def test_empty_batch_error() -> None:
         model(ts.io.atoms_to_state([], device="cpu", dtype=torch.float32))
 
 
+@pytest.mark.skipif(
+    get_token() is None, reason="Requires HuggingFace authentication for UMA model access"
+)
+def test_load_from_checkpoint_path(device: torch.device, dtype: torch.dtype) -> None:
+    """Test loading model from a saved checkpoint file path."""
+    checkpoint_path = pretrained_checkpoint_path_from_name("uma-s-1")
+    loaded_model = FairChemModel(
+        model=str(checkpoint_path), task_name="omat", cpu=device.type == "cpu"
+    )
+
+    # Verify the loaded model works
+    system = bulk("Si", "diamond", a=5.43)
+    state = ts.io.atoms_to_state([system], device=device, dtype=dtype)
+    results = loaded_model(state)
+
+    assert "energy" in results
+    assert "forces" in results
+    assert results["energy"].shape == (1,)
+    assert torch.isfinite(results["energy"]).all()
+    assert torch.isfinite(results["forces"]).all()
+
+
 test_fairchem_uma_model_outputs = pytest.mark.skipif(
     get_token() is None,
     reason="Requires HuggingFace authentication for UMA model access",

torch_sim/models/fairchem.py

@@ -8,6 +8,7 @@
 
 from __future__ import annotations
 
+import os
 import traceback
 import typing
 import warnings
@@ -74,6 +75,7 @@ def __init__(
         neighbor_list_fn: Callable | None = None,
         *,  # force remaining arguments to be keyword-only
         model_name: str | None = None,
+        model_cache_dir: str | Path | None = None,
         cpu: bool = False,
         dtype: torch.dtype | None = None,
         compute_stress: bool = False,
@@ -86,6 +88,7 @@ def __init__(
             neighbor_list_fn (Callable | None): Function to compute neighbor lists
                 (not currently supported)
             model_name (str | None): Name of pretrained model to load
+            model_cache_dir (str | Path | None): Path where to save the model
             cpu (bool): Whether to use CPU instead of GPU for computation
             dtype (torch.dtype | None): Data type to use for computation
             compute_stress (bool): Whether to compute stress tensor
@@ -132,7 +135,22 @@ def __init__(
         self.task_name = task_name
 
         # Create efficient batch predictor for fast inference
-        self.predictor = pretrained_mlip.get_predict_unit(str(model), device=device_str)
+        if model in pretrained_mlip.available_models:
+            if model_cache_dir and model_cache_dir.exists():
+                self.predictor = pretrained_mlip.get_predict_unit(
+                    model, device=device_str, cache_dir=model_cache_dir
+                )
+            else:
+                self.predictor = pretrained_mlip.get_predict_unit(
+                    model, device=device_str
+                )
+        elif os.path.isfile(model):
+            self.predictor = pretrained_mlip.load_predict_unit(model, device=device_str)
+        else:
+            raise ValueError(
+                f"Invalid model name or checkpoint path: {model}. "
+                f"Available pretrained models are: {pretrained_mlip.available_models}"
+            )
 
         # Determine implemented properties
         # This is a simplified approach - in practice you might want to