Toy Models

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 Models, but should satisfy the following requirements:

  1. Toy models can use any user species, but it recommended that if the model supports N species, it uses user01 to userN.

  2. 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 and their energy units as eV. From the perspective of the toy model these can be considered proxy units (similar to Lennard-Jones units).

  3. 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, …)).

  4. 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 KIM Items Browse Interface and sorting by species to find models that support species user01 to user20.