Iterative S-FFT phase refinement procedure. The initial phase values (φ) are combined with the experimental E amplitudes to give the initial ρ values (upper right corner). The ψ phases are obtained by Fourier transforming ρ2. Combination of ψ with the experimental (G − 〈G〉) gives the Fourier coefficients of the synthesis. The new structure factor estimates Q are obtained by Fourier transforming the δ·ρ product function.