diff --git a/simulation_structs.hpp b/simulation_structs.hpp
index 7f4b908..f1e267e 100755
--- a/simulation_structs.hpp
+++ b/simulation_structs.hpp
@@ -803,7 +803,10 @@ private:
         std::ifstream ifs(jsonFilepath);
         nlohmann::json json;
         ifs >> json;
-        internalPotentialEnergy = json.at(GET_VARIABLE_NAME(internalPotentialEnergy));
+        if (json.contains(GET_VARIABLE_NAME(internalPotentialEnergy))) {
+            internalPotentialEnergy = json.at(GET_VARIABLE_NAME(internalPotentialEnergy));
+        }
+        return true;
     }
 };