Dear Markus, Hamid recently pointed out to me that the OPTIMADE query: https://nomad-lab.eu/prod/rae/optimade/v1/structures?filter=elements%20HAS%20ALL%22Ni%22,%22O%22AND%20elements%20LENGTH2%20AND%20_nmd_dft_code_name=%20%22VASP%22&page_limit=40 returns: Status 500 title: "AttributeError" detail: "'NoneType' object has no attribute 'm_to_dict'" If I reduce the page limit to 28 or less, the query does work correctly. As the "page_offset" parameter does not work, I can however not obtain all the results from the database using optimade. Could you see what is wrong with your database/implementation? Kind regards, Johan Bergsma