The LCE is implemented in the LocalClusterExpansion class in kMCpy.model. The local environment in the LCE model is described using a migration unit (MigrationUnit), which is defined as a representative collection of sites centered around a given activated state (AS) where possible migration events can take place. The migration unit is generated using the user-specified cutoff radius. As a result, when a local environment is imported, an "occupation vector" (see Sec. A) will be constructed based on the atomic species at each site.