The Ewald method with electrostatic layer correction term for summing dipole-dipole interactions in slab geometry is presented. Theoretical cut-off errors in the electrostatic layer correction term as well as real- and reciprocal-space terms of the total energy are estimated, and their applicability is confirmed in numerical calculations. It is demonstrated that the summation method requires relative small gap of an empty space in the simulation box, and the theoretical errors can be used in determining optimal parameters of the method. (C) 2004 Elsevier B.V. All rights reserved.