diff --git a/mdagent/tools/base_tools/preprocess_tools/pdb_tools.py b/mdagent/tools/base_tools/preprocess_tools/pdb_tools.py
index 7233b199..00e8a457 100644
--- a/mdagent/tools/base_tools/preprocess_tools/pdb_tools.py
+++ b/mdagent/tools/base_tools/preprocess_tools/pdb_tools.py
@@ -471,10 +471,11 @@ def __init__(self, path_registry: typing.Optional[PathRegistry]):
         self.path_registry = path_registry
 
     def _get_sm_pdbs(self, small_molecules):
+        all_files = self.path_registry.list_path_names()
+        print(all_files)
         for molecule in small_molecules:
             # check path registry for molecule.pdb
-            exists = self.path_registry._check_json_content(molecule)
-            if not exists:
+            if molecule not in all_files:
                 # download molecule using small_molecule_pdb from MolPDB
                 molpdb = MolPDB()
                 molpdb.small_molecule_pdb(molecule, self.path_registry)
@@ -1575,7 +1576,7 @@ def smiles2name(self, smi: str) -> str:
             return "Unknown Molecule"
         return name
 
-    def small_molecule_pdb(self, mol_str: str, path_registry=None) -> str:
+    def small_molecule_pdb(self, mol_str: str, path_registry) -> str:
         # takes in molecule name or smiles (converts to smiles if name)
         # writes pdb file name.pdb (gets name from smiles if possible)
         # output is done message
@@ -1598,7 +1599,7 @@ def small_molecule_pdb(self, mol_str: str, path_registry=None) -> str:
             Chem.MolToPDBFile(m, file_name)
             # add to path registry
             if path_registry:
-                _ = path_registry.map_math(
+                _ = path_registry.map_path(
                     file_name, file_name, f"pdb file for the small molecule {mol_name}"
                 )
             return (
diff --git a/tests/test_fxns.py b/tests/test_fxns.py
index d4427749..92629d0d 100644
--- a/tests/test_fxns.py
+++ b/tests/test_fxns.py
@@ -1,5 +1,6 @@
 import json
 import os
+import time
 import warnings
 from unittest.mock import MagicMock, mock_open, patch
 
@@ -294,13 +295,13 @@ def test_map_path():
                 assert result == "Path successfully mapped to name: new_name"
 
 
-def test_small_molecule_pdb(molpdb):
+def test_small_molecule_pdb(molpdb, get_registry):
     # Test with a valid SMILES string
     valid_smiles = "C1=CC=CC=C1"  # Benzene
     expected_output = (
         "PDB file for C1=CC=CC=C1 successfully created and saved to benzene.pdb."
     )
-    assert molpdb.small_molecule_pdb(valid_smiles) == expected_output
+    assert molpdb.small_molecule_pdb(valid_smiles, get_registry) == expected_output
     assert os.path.exists("benzene.pdb")
     os.remove("benzene.pdb")  # Clean up
 
@@ -310,13 +311,13 @@ def test_small_molecule_pdb(molpdb):
     expected_output = (
         "There was an error getting pdb. Please input a single molecule name."
     )
-    assert molpdb.small_molecule_pdb(invalid_smiles) == expected_output
-    assert molpdb.small_molecule_pdb(invalid_name) == expected_output
+    assert molpdb.small_molecule_pdb(invalid_smiles, get_registry) == expected_output
+    assert molpdb.small_molecule_pdb(invalid_name, get_registry) == expected_output
 
     # test with valid molecule name
     valid_name = "water"
     expected_output = "PDB file for water successfully created and saved to water.pdb."
-    assert molpdb.small_molecule_pdb(valid_name) == expected_output
+    assert molpdb.small_molecule_pdb(valid_name, get_registry) == expected_output
     assert os.path.exists("water.pdb")
     os.remove("water.pdb")  # Clean up
 
@@ -342,9 +343,30 @@ def test_packmol_sm_download_called(packmol):
 
 
 def test_packmol_download_only(packmol):
+    path_registry = PathRegistry()
+    path_registry._remove_path_from_json("water.pdb")
+    path_registry._remove_path_from_json("benzene.pdb")
     small_molecules = ["water", "benzene"]
     packmol._get_sm_pdbs(small_molecules)
     assert os.path.exists("water.pdb")
     assert os.path.exists("benzene.pdb")
     os.remove("water.pdb")
     os.remove("benzene.pdb")
+
+
+def test_packmol_download_only_once(packmol):
+    path_registry = PathRegistry()
+    path_registry._remove_path_from_json("water.pdb")
+    small_molecules = ["water"]
+    packmol._get_sm_pdbs(small_molecules)
+    assert os.path.exists("water.pdb")
+    water_time = os.path.getmtime("water.pdb")
+    time.sleep(5)
+
+    # Call the function again with the same molecule
+    packmol._get_sm_pdbs(small_molecules)
+    water_time_after = os.path.getmtime("water.pdb")
+
+    assert water_time == water_time_after
+    # Clean up
+    os.remove("water.pdb")