DFT-optimized structures of the (10-12) tension twin boundary with a solute at different sites near the boundary. The dataset include the VASP input files (except POTCAR) and output files OSZICAR and OUTCAR. There are also text files containing the DFT-computed interaction energies between the twin boundary and the solutes at the different sites, and scripts that compute these energies from the raw DFT output. The README file contains expressions that can be used to compute the interaction energies and chemical misfit energies using the volumetric size misfit for any solute species in Mg.