diff --git a/src/nomad_parser_vasp/parsers/xml_parser.py b/src/nomad_parser_vasp/parsers/xml_parser.py
index bcc422e..dc3d85b 100644
--- a/src/nomad_parser_vasp/parsers/xml_parser.py
+++ b/src/nomad_parser_vasp/parsers/xml_parser.py
@@ -21,6 +21,8 @@
     'nomad_parser_vasp.parsers:xml_entry_point'
 )
 
+mix_alpha = lambda mix, cond: mix if cond else 0  # pylint: disable=W0613
+
 
 class VasprunXMLParser:
     def parse(
@@ -31,7 +33,6 @@ def parse(
         child_archives: 'dict[str, EntryArchive]' = None,
     ) -> None:
         logger.info(self.__class__.__name__, parameter=configuration.parameter)
-        mix_alpha = staticmethod(lambda mix, cond: mix if cond else 0)  # pylint: disable=W0613
 
         data_parser = MetainfoParser(annotation_key='xml', data_object=Simulation())
         XMLParser(filepath=mainfile).convert(data_parser)