diff --git a/tests/models/test_orb.py b/tests/models/test_orb.py
index 17a705f1..31901e16 100644
--- a/tests/models/test_orb.py
+++ b/tests/models/test_orb.py
@@ -1,6 +1,8 @@
 import traceback
 
+import numpy as np
 import pytest
+from ase.geometry.cell import cell_to_cellpar as ase_c2p
 
 from tests.conftest import DEVICE
 from tests.models.conftest import (
@@ -8,6 +10,8 @@
     make_model_calculator_consistency_test,
     make_validate_model_outputs_test,
 )
+from torch_sim import SimState
+from torch_sim.models.orb import cell_to_cellpar
 
 
 try:
@@ -74,3 +78,16 @@ def orbv3_direct_20_omat_calculator() -> ORBCalculator:
 test_validate_direct_model_outputs = make_validate_model_outputs_test(
     model_fixture_name="orbv3_direct_20_omat_model",
 )
+
+
+def test_cell_to_cellpar(ti_sim_state: SimState) -> None:
+    assert np.allclose(
+        ase_c2p(ti_sim_state.row_vector_cell.squeeze()),
+        cell_to_cellpar(ti_sim_state.row_vector_cell.squeeze(0)).cpu().numpy(),
+    )
+    assert np.allclose(
+        ase_c2p(ti_sim_state.row_vector_cell.squeeze(), radians=True),
+        cell_to_cellpar(ti_sim_state.row_vector_cell.squeeze(0), radians=True)
+        .cpu()
+        .numpy(),
+    )
diff --git a/torch_sim/models/orb.py b/torch_sim/models/orb.py
index 5ddb1d09..e3de08e0 100644
--- a/torch_sim/models/orb.py
+++ b/torch_sim/models/orb.py
@@ -29,7 +29,6 @@
 
 
 try:
-    from ase.geometry import cell_to_cellpar
     from orb_models.forcefield import featurization_utilities as feat_util
     from orb_models.forcefield.atomic_system import SystemConfig
     from orb_models.forcefield.base import AtomGraphs, _map_concat
@@ -59,6 +58,37 @@ def __init__(self, err: ImportError = exc, *_args: Any, **_kwargs: Any) -> None:
     from torch_sim.typing import StateDict
 
 
+def cell_to_cellpar(
+    cell: torch.Tensor,
+    radians: bool = False,  # noqa: FBT001, FBT002
+) -> torch.Tensor:
+    """Returns the cell parameters [a, b, c, alpha, beta, gamma].
+    torch version of ase's cell_to_cellpar.
+
+    Args:
+        cell:  lattice vector in row vector convention, same as ase
+        radians: If True, return angles in radians. Otherwise, return degrees (default).
+
+    Returns:
+        Tensor with [a, b, c, alpha, beta, gamma].
+    """
+    lengths = torch.linalg.norm(cell, dim=1)
+    angles = []
+    for i in range(3):
+        j = i - 1
+        k = i - 2
+        ll = lengths[j] * lengths[k]
+        if ll.item() > 1e-16:
+            x = torch.dot(cell[j], cell[k]) / ll
+            angle = 180.0 / torch.pi * torch.arccos(x)
+        else:
+            angle = 90.0
+        angles.append(angle)
+    if radians:
+        angles = [angle * torch.pi / 180 for angle in angles]
+    return torch.concat((torch.tensor(lengths), torch.tensor(angles)))
+
+
 def state_to_atom_graphs(  # noqa: PLR0915
     state: ts.SimState,
     *,
@@ -181,9 +211,7 @@ def state_to_atom_graphs(  # noqa: PLR0915
         num_edges.append(len(edges[0]))
 
         # Calculate lattice parameters
-        lattice_per_system = torch.from_numpy(
-            cell_to_cellpar(cell_per_system.squeeze(0).cpu().numpy())
-        )
+        lattice_per_system = cell_to_cellpar(cell_per_system.squeeze(0))
 
         # Create features dictionaries
         node_feats = {