for s 2 αβ = (s α +s β )/2. The power series expansions in these expressions are like equation (10), with different linear parameters {c i c,ss } and {c i c,ss }, and non-linear parameters γ c,ss = 0.02 and γ c,os = 0.006 respectively. These were fitted to the correlation energies of He and Ne. The same-and opposite-spin LSDA correlation energy densities per unit volume e LSDA c,σσ , e LSDA c,αβ are extracted from the total LSDA correlation energy density using: