Cutoff Radius Effect of Water Configuration Using the Wolf Method

Molecular dynamics simulation has been applied for water to compare the Wolf method to the IPS method and the Ewald sum by evaluating the diffusion coefficient and liquid structure. In our previous study, we applied the IPS method for bulk water and found notable deviation of the radial distribution function g(r). The Wolf method gives a good estimation for the potential energy and the self-diffusion coefficient at a cutoff radius, r_c, greater than 2.2 nm while avoiding the notable deviation of g(r) which appeared in the case of IPS. The distance dependent Kirkwood factor G_k(r) was also calculated, and the truncation of a long-range interaction of the cutofflike method (such as cutoff with or without the switch function and the reaction field) show serious shortcomings for dipole-dipole correlations in bulk water systems. This was observed by comparing the shape to that of the Ewald sum. G_k(r) of the cutofflike method greatly deviates from that of the Ewald sum. However, the discrepancy of G_k(r) for the Wolf method was found to be much less than that of other typical cutoff-like methods. We conclude that the Wolf method is an adequately accurate technique for estimating transport coefficients and the liquid structure of water in a homogeneous system at long cutoff distances.