The MDI package adds an mdi/engine command which enables LAMMPS to operate as a MolSSI Driver Interface (MDI) engine, responding to commands from an external MDI driver. It uses the MDI Library, which is available at https://github.com/MolSSI-MDI/MDI_Library. The MDI Library is developed and maintained by Taylor Barnes (tbarnes1@vt.edu) at the Molecular Sciences Software Institute (MolSSI). For more information about using MDI with LAMMPS, see the LAMMPS documentation for Howto_mdi in the Howto section. For general purpose information about MDI, see the MDI Library documentation: https://molssi-mdi.github.io/MDI_Library/html/index.html The MDI Library is required in order to use this package, and can be built using the Install.py file in lib/mdi as explained in lib/mdi/README. For example: python Install.py -m When using CMake to build LAMMPS the CMake configuration can use either a preinstalled MDI library or download and compile a private copy.