Pairwise long-range compensation for strongly ionic systems

We propose a pairwise compensation method for long-range electrostatics, as an alternative to traditional infinite lattice sums. The approach represents the third generation in a series beginning with the shifted potential corresponding to counterions surrounding a cutoff sphere. That simple charge compensation scheme resulted in pairwise potentials that are continuous at the cutoff, but forces that are not. A second-generation approach modified both the potential and the force such that both are continuous at the cutoff. Here we introduce another layer of softening such that the derivative of the force is also continuous at the cutoff. In strongly ionic liquids, this extension removes structural artifacts associated with the earlier pairwise compensation schemes, and provides results that compare well with Ewald sums.