View source for F(000)


The expression for a [[structure factor]] evaluated in the zeroth-order case <math>h=k=l=0</math> yields the result

<math>F(000) = [ (\sum f_{r} )^{\,2} + (\sum f_{i}
)^{\,2} ]^{1/2}</math>

where <math>f_{r}</math> is the real part of the scattering factors at <math>\theta = 0^\circ</math>, <math>f_{i}</math> is the  imaginary part of the scattering factors at <math>\theta = 0^\circ</math>, <math>\theta</math> is the [[Bragg angle]], and the sum is taken over each atom in the unit cell.

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

For X-rays non-dispersive <math>F(000)</math> 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 <math>F(000)</math> is either positive or negative and counts the total nuclear scattering power in the cell.

[[Category:Structure determination]]
[[Category:X-rays]]