The extended Ewald method: A general treatment of long-range electrostatic interactions in microscopic simulations

The Ewald method, which is known as a method for evaluating electrostatic interactions in periodic systems, is extended to nonperiodic systems. A general way of applying the Ewald method to nonperiodic systems is described and a detailed application is demonstrated for the treatment of ions immersed in dipolar solvent molecules. As a preliminary test, electric fields produced by point dipoles forming a simple cubic lattice are calculated, both by the new Ewald treatment and by the conventional cutoff (truncation) method. These test calculations not only demonstrate the advantage of the new Ewald method but also reveal inherent problems associated with the cutoff method.