diff --git a/config/proxy/crystals/phast_pyxtal.yaml b/config/proxy/crystals/phast_pyxtal.yaml
deleted file mode 100644
index 92e5e8c69..000000000
--- a/config/proxy/crystals/phast_pyxtal.yaml
+++ /dev/null
@@ -1 +0,0 @@
-_target_: gflownet.proxy.crystals.phast_pyxtal.PhastPyxtal
diff --git a/config/proxy/crystals/pyxtal_gnn.yaml b/config/proxy/crystals/pyxtal_gnn.yaml
new file mode 100644
index 000000000..ef9c059af
--- /dev/null
+++ b/config/proxy/crystals/pyxtal_gnn.yaml
@@ -0,0 +1 @@
+_target_: gflownet.proxy.crystals.pyxtal_gnn.PyxtalGNN
diff --git a/gflownet/proxy/crystals/pyxtal_gnn.py b/gflownet/proxy/crystals/pyxtal_gnn.py
new file mode 100644
index 000000000..80921f363
--- /dev/null
+++ b/gflownet/proxy/crystals/pyxtal_gnn.py
@@ -0,0 +1,170 @@
+import torch
+from torchtyping import TensorType
+
+from gflownet.proxy.base import Proxy
+from gflownet.utils.common import tfloat
+
+import pyxtal
+from pyxtal.lattice import Lattice
+from pyxtal.msg import Comp_CompatibilityError
+from pyxtal.symmetry import Group
+
+
+def is_valid_crystal(
+    space_group, elements, num_ions, a, b, c, alpha, beta, gamma
+) -> bool:
+    """Determines if a crystal is valid
+
+    This function may not catch all instances of invalid crystals so return value
+    of True should not be taken as a garantee of validity but, rather, as an
+    indication that this limited function didn't find an issue with the crystal
+    """
+    # Validate that lengths are strictly positive
+    for length in [a, b, c]:
+        if length <= 0:
+            return False
+
+    # Validate that angles are individually reasonnable
+    for angle in [alpha, beta, gamma]:
+        if angle <= 0 or angle >= 180:
+            return False
+
+    # Validate that the angles can be use together to create a unit cell with
+    # non-zero, non-imaginary volume.
+    if a + b + c >= 360:
+        return False
+    elif a + b - c <= 0:
+        return False
+    elif a + c - b <= 0:
+        return False
+    elif b + c + a <= 0:
+        return False
+
+    return True
+
+
+class PyxtalGNN(Proxy):
+    """
+    Proxy using a GNN model to evaluate samples.
+
+    This proxy assumes that the samples do not contain atom coordinates and
+    therefore uses PyXtal to sample atom coordinates before feeding the samples
+    to the GNN model.
+    """
+
+    ENERGY_INVALID_SAMPLE = 10
+
+    def __init__(self, n_pyxtal_samples=1, **kwargs):
+        super().__init__(**kwargs)
+        self.n_pyxtal_samples = n_pyxtal_samples
+
+    @torch.no_grad()
+    def __call__(self, states: TensorType["batch", "elements"]) -> TensorType["batch"]:
+        """
+        Forward pass of the proxy.
+
+        Args:
+            states (torch.Tensor): States to infer on. Shape:
+                ``(batch, [n_elements + 1 + 6])``.
+
+        Returns:
+            torch.Tensor: Proxy energies. Shape: ``(batch,)``.
+        """
+        y = [self.evaluate_state(s) for s in states.numpy()]
+        return tfloat(y, states.device, states.dtype)
+
+    def evaluate_state(self, state) -> float:
+
+        # Obtain composition, space group and lattice parameters from the state
+        composition = state[:-7].astype("int32")
+        space_group_idx = state[-7].astype("int32")
+        a, b, c, alpha, beta, gamma = state[-6:]
+
+        # Compute the list of elements and number of atoms per element
+        elements = []
+        atoms_per_element = []
+        for atomic_number, nb_atoms in enumerate(composition):
+            if nb_atoms > 0:
+                elements.append(atomic_number)
+                atoms_per_element.append(nb_atoms.item())
+
+        # If something in the crystal is identified to be invalid, skip the process of
+        # generating atom coordinated with PyXtal and return a default high energy for
+        # invalid crystals
+        if not is_valid_crystal(
+            space_group_idx, elements, atoms_per_element, a, b, c, alpha, beta, gamma
+        ):
+            return self.ENERGY_INVALID_SAMPLE
+
+        # Generate crystal samples with atom positions using PyXtal
+        pyxtal_samples = self.generate_pyxtal_samples(
+            space_group_idx, elements, atoms_per_element, a, b, c, alpha, beta, gamma
+        )
+
+        # Score the PyXtal samples using the proxy
+        # TODO : If possible, process the PyXtal samples in batches
+        if len(pyxtal_samples) > 0:
+            pyxtal_sample_scores = []
+            for sample in pyxtal_samples:
+                # Convert the PyXtal crystal to the graph format expected by the model
+                sample_graph = self.graph_from_pyxtal(sample)
+
+                # Score the sample using the model
+                sample_score = self.energy_from_graph(sample_graph)
+                pyxtal_sample_scores.append(sample_score)
+
+            global_sample_score = min(pyxtal_sample_scores)
+
+        else:
+            # PyXtal was unable to generate valid crystals given the state. Provide a
+            # default bad score.
+            global_sample_score = self.ENERGY_INVALID_SAMPLE
+
+        return global_sample_score
+
+    def graph_from_pyxtal(self, pyxtal_crystal):
+        return None #TODO
+
+    def energy_from_graph(self, graph):
+        return 0 #TODO
+
+    def generate_pyxtal_samples(
+        self, space_group_idx, elements, atoms_per_element, a, b, c, alpha, beta, gamma
+    ):
+
+        # Instantiate space group
+        space_group = Group(space_group_idx)
+
+        # Create a lattice of the appropriate type
+        lattice = Lattice.from_para(
+            a, b, c, alpha, beta, gamma, ltype=space_group.lattice_type
+        )
+
+        pyxtal_samples = []
+        for i in range(self.n_pyxtal_samples):
+            try:
+                crystal = pyxtal.pyxtal()
+                crystal.from_random(
+                    dim=3,
+                    group=space_group,
+                    species=elements,
+                    numIons=atoms_per_element,
+                    lattice=lattice
+            )
+            except Comp_CompatibilityError:
+                # PyXtal deems the composition incompatible with the space
+                # group. PyXtal is sometimes wrong on this but, at any rate,
+                # we can't general crystals using PyXtal for this sample. Skip.
+                continue
+
+            # Validate the produced crystal
+            if crystal.valid:
+                pyxtal_samples.append(crystal)
+
+        return pyxtal_samples
+
+
+    def pyxtal2proxy(self, pyxtal_crystal):
+        # TODO
+        return None
+