  We present a data set from a first-principles study of amino-methylated and
acetylated (capped) dipeptides of the 20 proteinogenic amino acids - including
alternative possible side chain protonation states and their interactions with
selected divalent cations (Ca$^{2+}$, Mg$^{2+}$ and Ba$^{2+}$). The data covers
21,909 stationary points on the respective potential-energy surfaces in a wide
relative energy range of up to 4 eV (390 kJ/mol). Relevant properties of
interest, like partial charges, were derived for the conformers. The motivation
was to provide a solid data basis for force field parameterization and further
applications like machine learning or benchmarking. In particular the process
of creating all this data on the same first-principles footing, i.e.
density-functional theory calculations employing the generalized gradient
approximation with a van der Waals correction, makes this data suitable for
data-driven force field development. To make the data accessible across domain
borders and to machines, we formalized the metadata in an ontology.
