The Sphere Resolution determines how finely to tessellate the spheres that are drawn, when using rendering modes and external rendering tools that can only draw polygonal geometry. The performance of polygonal sphere rendering varies inversely with the number of triangles produced by tessellation into triangles. The number of triangles per sphere varies proportionally with the Sphere Resolution parameter value squared. For rendering modes such as GLSL, and for external rendering tools that can directly represent spheres and other quadric surfaces, the Sphere Resolution parameter has no effect.
Note: Due to variations in atom naming conventions, in rare instances VMD may improperly assign VDW radii to specific atoms, since VMD determines each atom type based on the first letter forming its name. For example, VMD would assume an atom named ``HG'' to be a hydrogen rather than a mercury. If this happens, you are always free to redefine the radii, using a syntax much like that below:
set sel [atomselect top ``name HG''] $sel set radius 1.9