diff --git a/ramannoodle/polarizability/torch/gnn.py b/ramannoodle/polarizability/torch/gnn.py
index 4decc52..8c5cabf 100644
--- a/ramannoodle/polarizability/torch/gnn.py
+++ b/ramannoodle/polarizability/torch/gnn.py
@@ -37,7 +37,7 @@
 # pylint: disable=not-callable
 
 
-class GaussianFilter(torch.nn.Module):
+class _GaussianFilter(torch.nn.Module):
     """Gaussian filter.
 
     Parameters should be chosen such that all expected inputs are between lower and
@@ -75,7 +75,7 @@ def forward(self, x: Tensor) -> Tensor:
         return torch.exp(self.coefficient * x.pow(2))
 
 
-class NodeBlock(torch.nn.Module):
+class _NodeBlock(torch.nn.Module):
     """Edge to node message passer.
 
     Architecture and notation is based on equation (5) in https://doi.org/10.1038/
@@ -144,7 +144,7 @@ def forward(
         return typing.cast(Tensor, (node_embedding + c1_emb).tanh())
 
 
-class EdgeBlock(torch.nn.Module):
+class _EdgeBlock(torch.nn.Module):
     """Node to edge message passer.
 
     Architecture and notation is based on equation (6) in https://doi.org/10.1038/
@@ -442,6 +442,21 @@ def __init__(  # pylint: disable=too-many-arguments,too-many-instance-attributes
         gaussian_filter_end: float,
     ):
         super().__init__()
+        # Validate parameters
+        if cutoff <= 0:
+            raise ValueError(f"invalid cutoff: {cutoff} <= 0")
+        if size_node_embedding <= 0:
+            raise ValueError(f"invalid size_node_embedding: {size_node_embedding} <= 0")
+        if size_edge_embedding <= 0:
+            raise ValueError(f"invalid size_edge_embedding: {size_edge_embedding} <= 0")
+        if num_message_passes <= 0:
+            raise ValueError(f"invalid num_message_passes: {num_message_passes} <= 0")
+        if gaussian_filter_start <= 0:
+            inequality = f"{gaussian_filter_start} <= 0"
+            raise ValueError(f"invalid gaussian_filter_start: {inequality}")
+        if gaussian_filter_end <= gaussian_filter_start:
+            inequality = f"{gaussian_filter_end} <= gaussian_filter_start"
+            raise ValueError(f"invalid gaussian_filter_end: {inequality}")
 
         self._ref_structure = ref_structure
         self._cutoff = cutoff
@@ -472,19 +487,19 @@ def __init__(  # pylint: disable=too-many-arguments,too-many-instance-attributes
             ShiftedSoftplus(),
             Linear(size_node_embedding, size_node_embedding),
         )
-        self._edge_embedding = GaussianFilter(
+        self._edge_embedding = _GaussianFilter(
             gaussian_filter_start, gaussian_filter_end, size_edge_embedding
         )
 
         self._node_blocks = ModuleList(
             [
-                NodeBlock(size_node_embedding, size_edge_embedding)
+                _NodeBlock(size_node_embedding, size_edge_embedding)
                 for _ in range(num_message_passes)
             ]
         )
         self._edge_blocks = ModuleList(
             [
-                EdgeBlock(size_node_embedding, size_edge_embedding)
+                _EdgeBlock(size_node_embedding, size_edge_embedding)
                 for _ in range(num_message_passes)
             ]
         )