where a σ = ω/k F,σ , and k F,σ = [6π 2 ρ σ ] 1/3 is the spin-polarized Fermi wave vector. The original range-separation scheme consists of short-range density-functional exchange and long-range HF exchange, with no HF exchange at short range. It has been shown that including a small fraction c sr x of short-range HF exchange in addition to the short-range DFT exchange is beneficial without affecting the correct long-range behavior. While the LSDA exchange functional is helpful to illustrate range-separation in exchange functionals, it is not suitable for most applications due to the homogeneous nature of the functional. A better approach is to use a GGA functional for the density functional exchange component. The B97 functional uses a power series expansion involving the density and its first derivative: 30