# F(000)

$F(000) = [ (\sum f_{r} )^{\,2} + (\sum f_{i} )^{\,2} ]^{1/2}$
where fr is the real part of the scattering factors at $\theta = 0^\circ$, fi is the imaginary part of the scattering factors at $\theta = 0^\circ$, θ is the Bragg angle, and the sum is taken over each atom in the unit cell.