where E HF c,∞ , E HF 1/2 and E HF 3/4 are functionals of the HF density. Because the functionals on the right-hand side of Eqs. 5 and 6 depend on HF orbitals and densities , they provide a basis for constructing approximate MPAC functionals that interpolate between the small-λ and large-λ limits using only HF-density/orbital inputs .