Since we are considering molecular volume overlap as a measure, the radii used for each atom is important. There are essentially 2 settings. A radii approximation of All means each atom will be treated with the radius as passed in. Alternatively, one can treat all heavy atoms as similar and apply the Carbon radius approximation. With this, all heavy atoms will be assigned the same radius, regardless of the value attached to each atom. As noted above, if the Grid method is chosen, the Carbon radius approximation is also turned on.