# F(000)

### From Online Dictionary of Crystallography

The expression for a structure factor evaluated in the zeroth-order case *h* = *k* = *l* = 0 yields the result

where *f*_{r} is the real part of the scattering factors at , *f*_{i} is the imaginary part of the scattering factors at , θ is the Bragg angle, and the sum is taken over each atom in the unit cell.

*F*(000) is computed without dispersion effects in electron-density calculation by Fourier inversion. In all cases, non-dispersive *F*(000) is a structure factor and not a
structure amplitude: it has both magnitude and a sign.

For X-rays non-dispersive *F*(000) is positive definite and in many cases an integer (but it is not an integer for non-stoichiometric compounds). It counts the number of electrons in the cell.

For neutrons non-dispersive *F*(000) is either positive or negative and counts the total nuclear scattering power in the cell.