Specify the size of the support (i.e., the rate of change) for spline-based surface definitions (see srfm). Usually 0.3 Å. The syntax is:

   swin {win}

where win is a floating point number for the spline window width (in Å). Note that, per the analysis of Nina, Im, and Roux (doi:10.1016/S0301-4622(98)00236-1), the force field parameters (radii) generally need to be adjusted if the spline window is changed.