The loose-coupling model used in the MiMiC framework requires communication of data, e.g. atomic positions and forces, between the coupled programs, which are running independently. To achieve this objective MiMiC provides a communication library (CommLib), which has been designed to minimize the coding effort in the external programs used by the MiMiC framework. In fact, CommLib does not interfere with preexisting communication layers within the coupled programs, e.g. their MPI parallelization scheme does not need to be altered. In practice, one simply invokes the send and/or receive routines in CommLib to exchange data between two programs using an ID associated to a specific domain of the multiscale representation (e.g. QM, MM, etc.) which is created during the CommLib initialization.