code: private static Shape createAtomHighlight(IAtom atom, double radius) {
          double x = atom.getPoint2d().x;
          double y = atom.getPoint2d().y;
  
          return new RoundRectangle2D.Double(x - radius, y - radius, 2 * radius, 2 * radius, 2 * radius, 2 * radius);
      }
docs: Create the shape which will highlight the provided atom.
  
  @param atom   the atom to highlight
  @param radius the specified radius
  @return the shape which will highlight the atom