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
mp-804, while zinc blende GaN is assigned a
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_idwill then become the
material_id. This ensures that, as new, additional calculations are associated with the same material, its
material_idshould not change.
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_idcannot change, but a
material_idwill now always start with an
mp-prefix by convention provided that at least one task associated with that material has the
task_idwill never change. It will always refer to the same, individual calculation task.
material_idmight change in rare instances, such as the removal of the
mvc-prefix, although this is avoided wherever possible.
material_iddoes change, we ensure a redirect on the website is always in place, and the new
material_idcan 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_idare still valid, and the relevant data can still be retrieved.