diff --git a/src/pymdgen/__init__.py b/src/pymdgen/__init__.py
index 184a0de..847ed58 100644
--- a/src/pymdgen/__init__.py
+++ b/src/pymdgen/__init__.py
@@ -36,8 +36,16 @@ def getargspec(func):
     decorated functions
     """
     if hasattr(func, "__wrapped__"):
-        return inspect.getfullargspec(func.__wrapped__)
-    return inspect.getfullargspec(func)
+        func = func.__wrapped__
+
+    sig = inspect.signature(func)
+    return [
+        list(sig.parameters),
+        None,
+        None,
+        [param.default for param in sig.parameters.values() if param.default != inspect.Parameter.empty],
+    ]
+
 
 
 def doc_func(name, func, section_level=4):
diff --git a/src/pymdgen/test_getargspec.py b/src/pymdgen/test_getargspec.py
new file mode 100644
index 0000000..278f2a8
--- /dev/null
+++ b/src/pymdgen/test_getargspec.py
@@ -0,0 +1,45 @@
+import inspect
+from functools import wraps
+from pymdgen import getargspec # Import your __init__.py module
+
+
+def test_getargspec_simple_function():
+    def my_function(a, b, c=10):
+        pass
+    expected_result = [
+        ['a', 'b', 'c'], 
+        None, 
+        None, 
+        [10,],
+    ]
+    assert getargspec(my_function) == expected_result
+
+def test_getargspec_args_kwargs():
+    def my_function(a, b, *args, **kwargs):
+        pass
+    expected_result = [
+        ['a', 'b', 'args', 'kwargs'], 
+        None, 
+        None, 
+        [],
+    ]
+    assert getargspec(my_function) == expected_result
+
+def test_getargspec_decorated_function():
+    def my_decorator(func):
+        @wraps(func)
+        def wrapper(*args, **kwargs):
+            return func(*args, **kwargs)
+        return wrapper
+
+    @my_decorator
+    def my_function(a, b, c=20):
+        pass
+
+    expected_result = [
+        ['a', 'b', 'c'], 
+        None, 
+        None, 
+        [20,],
+    ]
+    assert getargspec(my_function) == expected_result
\ No newline at end of file