We extend the recent formulation of the Ewald sum for electrostatics in a two-dimensionally periodic three-dimensional multiatom layer or two-dimensional single-atom layer system with a rectangular periodic boundary condition(J Chem Theory Comput, 2014, 10: 534–542) to that with a parallelogrammic periodic boundary condition in general. Following the discussion of an efficient implementation of the formula, we suggest a simple setup of parameters using a relatively smaller screening factor and the associated larger real space cutoff distance to reach an optimized algorithm of an order N computational cost. The connection between the previous application of the Ewald sum to ionic crystal systems and the future application to molecular self-assembly or disassembly systems on solid surfaces or at liquid-liquid interfaces are illustrated to demonstrate the applicability of the present work to simulate the self-assembly process and to produce dynamical, structural and thermodynamic properties of experimental self-assembly systems of interest. We extend the recent formulation of the Ewald sum for electrostatics in a two-dimensionally periodic three-dimensional multiatom layer or two-dimensional single-atom layer system with a rectangular periodic boundary condition (J Chem Theory Comput, 2014, 10: 534-542 Following the discussion of an efficient implementation of the formula, we suggest a simple setup of parameters using a relatively smaller screening factor and the associated larger real space cutoff distance to reach an optimized algorithm of an order N computational cost. The connection between the previous application of the Ewald sum to ionic crystal systems and the future application to molecular self-assembly or disassembly systems on solid surfaces or at liquid-liquid interfaces are illustrated to demonstrate the applicability of the present work to simulate the self-assembly process and to produce dynamical, structural and thermodynamic proper ties of experimental self-assembly systems of interest.