diff --git a/bin/emle-server b/bin/emle-server
index d724ee8..e6fb8e2 100755
--- a/bin/emle-server
+++ b/bin/emle-server
@@ -183,6 +183,7 @@ parser.add_argument(
     "--features",
     type=str,
     help="the type of feature used by the model ('soap' or 'aev')",
+    choices=["soap", "aev"],
     required=False,
 )
 parser.add_argument(
diff --git a/emle/calculator.py b/emle/calculator.py
index 055d856..e22bba7 100644
--- a/emle/calculator.py
+++ b/emle/calculator.py
@@ -1158,6 +1158,8 @@ def __init__(
                 "cuda" if _torch.cuda.is_available() else "cpu"
             )
 
+        if features is None:
+            features = "soap"
         if not isinstance(features, str):
             msg = "'features' must be of type 'str'"
             _logger.error(msg)