def METHOD_NAME(self, pacs_name):
    """
    Overriden to check whether the provided PACS name is a valid PACS identifier.
    """
    try:
        PACS.objects.get(identifier=pacs_name)
    except PACS.DoesNotExist:
        # validate new PACS identifier
        pacs_serializer = PACSSerializer(data={'identifier': pacs_name})
        try:
            pacs_serializer.is_valid(raise_exception=True)
        except serializers.ValidationError as e:
            raise serializers.ValidationError(e.detail['identifier'])
    return pacs_name