The key MRF building blocks described in the previous subsection and the MRF functional itself are implemented in a development version of the TURBOMOLE program . The MRF XC energy densities (Eq. 8) are calculated on the usual real-space grids for semilocal XC functionals. At each grid point r, we calculate the N e (r, u) integral (the key MRF ingredient) and ρ r, u (needed for the MRF's fluctuation functions that employ S i (r) of Eq. 12). Both N e (r, u) and ρ r, u are precomputed for a range of u interelectronic distances. Then the MRF energy density is computed following a stepwise procedure: