We use first-principles energy density method (EDM) to calculate atomic energies for isolated ⟨𝑎⟩-type basal and prism screw dislocation cores in Mg and compute line energies and core energy differences. The atomic energy distribution in the dislocations reflect the slip in the cores and the elastic energy further afield. Line energies are computed by summing up atomic energies

from which core energies and energy differences are straightforward to determine. We compare our results with two different classical potentials.