material_id (also referred to in various places as mp-id, mpid, MPID). This allows a specific polymorph of a given material to be referenced. For example, wurtzite GaN is assigned the material_id of mp-804, while zinc blende GaN is assigned a material_id of mp-830.mp-[0-9] ("mp-" with numbers after it). These identifiers are assigned sequentially, so smaller numbers usually refer to older calculations. An identifier referring to an individual calculation task are known as a task_id.task_id will then become the material_id. This ensures that, as new, additional calculations are associated with the same material, its material_id should not change.mvc- instead of mp- and thus some materials also had the prefix mvc-. However, this caused confusion and this approach has been retired. Tasks with the prefix mvc- still exist since the task_id cannot change, but a material_id will now always start with an mp- prefix by convention provided that at least one task associated with that material has the mp- prefix.task_id will never change. It will always refer to the same, individual calculation task.material_id might change in rare instances, such as the removal of the mvc- prefix, although this is avoided wherever possible.material_id does change, we ensure a redirect on the website is always in place, and the new material_id can also be found programmatically with the API using the get_material_id_from_task_id() function. This way, any publications or research that reference an older material_id are still valid, and the relevant data can still be retrieved.