Energy density analysis (EDA), which partitions the total energy of a molecular system into atomic energy densities, has been proposed in order to analyze local energy changes. This study extends the formulation of the EDA technique to extended systems, of which electronic structures are calculated under the periodic boundary condition; i.e., PBC-EDA. Numerical applications to MgO(100) and (m10) (m = 1-6) surfaces confirm the reliability and usefulness of PBC-EDA. In particular, site-dependent atomization energies evaluated by PBC-EDA are clarified to be important in comparing with bulk properties and in examining stability and/or reactivity of surface sites. (c) 2007 Elsevier B.V. All rights reserved.