diff --git a/janus_core/geom_opt.py b/janus_core/geom_opt.py
index 9753f6b2..de6cef4e 100644
--- a/janus_core/geom_opt.py
+++ b/janus_core/geom_opt.py
@@ -34,22 +34,22 @@ def optimize(
     fmax : float
         Set force convergence criteria for optimizer in units eV/Å.
     dyn_kwargs : Optional[dict[str, Any]]
-        kwargs to pass to dyn.run. Default is None.
+        kwargs to pass to dyn.run. Default is {}.
     filter_func : Optional[callable]
         Apply constraints to atoms through ASE filter function.
         Default is `FrechetCellFilter`.
     filter_kwargs : Optional[dict[str, Any]]
-        kwargs to pass to filter_func. Default is None.
+        kwargs to pass to filter_func. Default is {}.
     optimzer : callable
         ASE optimization function. Default is `LBFGS`.
     opt_kwargs : Optional[dict[str, Any]]
-        kwargs to pass to optimzer. Default is None.
+        kwargs to pass to optimzer. Default is {}.
     struct_kwargs : Optional[dict[str, Any]]
         kwargs to pass to ase.io.write to save optimized structure.
-        Must include "filename" keyword. Default is None.
+        Must include "filename" keyword. Default is {}.
     traj_kwargs : Optional[dict[str, Any]]
         kwargs to pass to ase.io.write to save optimization trajectory.
-        Must include "filename" keyword. Default is None.
+        Must include "filename" keyword. Default is {}.
 
     Returns
     -------
diff --git a/janus_core/single_point.py b/janus_core/single_point.py
index f0b5cb70..5942ae42 100644
--- a/janus_core/single_point.py
+++ b/janus_core/single_point.py
@@ -33,7 +33,7 @@ def __init__(
         device : str
             Device to run model on. Default is "cpu".
         read_kwargs : Optional[dict[str, Any]]
-            kwargs to pass to ase.io.read. Default is None.
+            kwargs to pass to ase.io.read. Default is {}.
         """
         self.architecture = architecture
         self.device = device
@@ -61,7 +61,7 @@ def set_calculator(
         Parameters
         ----------
         read_kwargs : Optional[dict[str, Any]]
-            kwargs to pass to ase.io.read. Default is None.
+            kwargs to pass to ase.io.read. Default is {}.
         """
         calculator = choose_calculator(
             architecture=self.architecture,