// Last edited on 2019-04-05 18:06:16 by stolfi

#macro ion(ctr,rad,N,Q)
  // Ion with center {ctr}, radius {rad}, atomic number {N},
  // and charge {Q} (may be fractional).
  // The charge is displayed as a foggy ball surrounding the atom
  // with radius and intensity that increases monotonically with {Q},
  // up to a maximum .
  #if (Q == 0)
    object{ atom(ctr,rad,N)
  #else
    union{
      atom(ctr,rad,N);
      object{ halo(ctr,rad,Q) }
    }
  #end
#end