Calculation of long-range interactions in molecular dynamics and Monte Carlo simulations

The general expansion method is developed to calculate long-range interactions due to charged particles outside the minimum images, for different periodic systems in molecular dynamics and Monte Carlo simulations. The expansion coefficients are obtained by the least-squares method. The neighbor-box technique is also developed to calculate long- and short-range interactions within the minimum images. The interactions between neighbor particles are directly calculated, while the interactions between nonneighbor particles are obtained by interpolation. The combination of the general expansion (GE) method and the neighbor-box (NB) technique, named as the GENE method, renders the computation of long-range interactions proportional to N-3/2, where N is the total number of particles in the central cell. Most importantly, the GENE method can be easily used to study different periodic systems. As an example, water molecules in a cylindrical pore are simulated to demonstrate the computational efficiency and accuracy of the neighbor-box technique under different conditions.