The core structures of < c + a > edge and screw dislocations in Mg are computed using density functional theory (DFT). Both types dissociate into two 1/2 < c + a > partials on the second-order pyramidal planes. These DFT results are then allowed to relax with embedded-atom and modified embedded-atom (MEAM) potentials. Only MEAM retains the general structure of the DFT predictions. The DFT core structures provide the basis for future investigations of solute effects and calibration of interatomic potentials. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.