Materials Databases Ontology (OPTIMADE)

Formal definiion: A material is something that is described by a materials model. Physical description: A material is a system of atoms in a state described by a statistical distribution over 'microstates' (microscopic structure realizations). A material is distinguished from other materials by the ensemble of microstates that, due to the statistical distribution, are effectively the relevant ones in observations of the system. Two systems with distinctively different ensembles of relevant microstates are two different materials. For a system of atoms in an environment that changes (e.g. the temperature, pressure, etc.) the ensemble of relevant microstates may change. This can happen discontinuously, which represents a phase transition, or continuously over a path in the phase diagram. The ensemble of relevant microstates may contain only a single microstate. This is, depending on the periodicity, the representation of a perfect bulk single crystal, slab, wire or molecule. While the ensemble of relevant microstates defines the specific material, a material can be specified without explicitly specifying this ensemble of microstates via a materials model. Such models include the description of the material as a composite, a metallic alloy, an amorphous structure, a quasicrystal, or as the result of a synthesis process.

Material