Ewald artifacts in liquid state molecular dynamics simulations

An investigation into the effects of the anisotropic nature of the Ewald potential, for the treatment of long range electrostatic interactions in liquid solutions has been performed. The rotational potential energy surface for two simple charge distributions, and a small protein, have been studied under conditions typically implemented in current biomolecular simulations. A transition between hindered and free rotation is observed which can be modeled quantitatively for simple charge distributions. For most systems in aqueous solution, the transition involves an energy change well below k_BT. It is argued that, for solvents with a reasonably high relative permittivity, Ewald artifacts will be small and in many cases may be safely ignored.