For each cluster of a given number of atoms N and element type k, the database contains the energy relative to the lowest energy structure of size N and species k, the formation energy with respect to the stable cluster of size N-1 of species k (equation ( )), the formation energy with respect to the N+1 stable cluster of the same species (equation ( )), the HOMO-LUMO gap, the number of valence electrons considered by DFT, the magnetic moment, a list of similar structures within the Quantum Cluster Database, a list of literature references for the cluster (downloadable in .bib format), the coordinates (downloadable in XYZ format), and an interactive visualization of the cluster. The formation energies are calculated using the following equations: