Real space R factor of electron density for all atoms.
      The real space R factor is calculated by the equation
      R_real = [Sumi (|Dobs - Dcal|)]/[Sumi (|Dobs + Dcal|)]
      Where:
         Dobs is the observed  electron density,
         Dcal is the calculated  electron density,
              summation is for all the grid points
      Ref: Branden, C.I. & Jones, T.A. (1990).  Nature, 343, 687-689