diff --git a/pymatgen/io/qchem/sets.py b/pymatgen/io/qchem/sets.py
index dbba6a31f71..93436e34db3 100644
--- a/pymatgen/io/qchem/sets.py
+++ b/pymatgen/io/qchem/sets.py
@@ -500,6 +500,9 @@ def __init__(
                     nbo[key] = self.nbo_params[key]
 
         tmp_geom_opt = self.geom_opt
+        if tmp_geom_opt is not None and "initial_hessian" in tmp_geom_opt:
+            if tmp_geom_opt["initial_hessian"] == "deleted":
+                del tmp_geom_opt["initial_hessian"]
         geom_opt = self.geom_opt
         if (self.job_type.lower() in ["opt", "optimization"] and self.qchem_version == 6) or (
             self.qchem_version == 5 and self.geom_opt is not None
@@ -517,6 +520,8 @@ def __init__(
                 if self.qchem_version == 6:
                     if "coordinates" not in tmp_geom_opt:
                         tmp_geom_opt["coordinates"] = "redundant"
+                    elif tmp_geom_opt["coordinates"] == "delocalized" and "initial_hessian" not in tmp_geom_opt:
+                        tmp_geom_opt["initial_hessian"] = "model"
                     if "max_displacement" not in tmp_geom_opt:
                         tmp_geom_opt["max_displacement"] = "0.1"
                     if "optimization_restart" not in tmp_geom_opt: