Interatomic models are normally designed to simulate real material systems.
However OpenKIM also supports the notion of a "toy model." In physics,
a toy model is defined as "a deliberately simplistic model
with many details removed so that it can be used to explain a mechanism
concisely" [Wikipedia].
In molecular simulations, a toy model is an interatomic potential that
is not designed to model a real material, but rather associated with a class
of materials (e.g. glasses). Such models are used extensively in materials
simulations to understand qualitiative features of material behavior.
To support toy models, the KIM API provides user species
(user01-user20).
Toy models can be uploaded to openkim.org as KIM Portable Models, but should satisfy the following requirements:
Toy models can use any user species, but it recommended that if the
model supports N species, it uses user01 to userN.
Some toy models are formulated to be nondimensional. Rather than
introducing a new type of nondimensional units to the KIM API with
accompanying requirements for simulators to support this, toy models are
required to define their length units as A (Angstrom) and their energy
units as eV. From the perspective of the toy model these can be
considered proxy units (similar to Lennard-Jones units).
Toy models uploaded to openkim.org are subjected to all verification
checks and all tests that are compatible with them (i.e. designed to run
with their species (user01, …)).
Toy models have model pages just like all KIM Models. They also have in-line visualizers that compare the predictions of different toy models that support the same user species. On the face of it such comparisons are meaningless since there is no agreement between toy models on the identity of user species, however this information can be used in a different way. It allows users to select toy models that have specific properties that they are interested in.
Toy models in openkim.org can be found using the
browse interface
and sorting by species to find models that support species user01 to user20.