**Definition:**

The effective number of electrons in the crystal unit cell contributing to F(000). This may contain dispersion contributions and is calculated as F(000) = [ (sum f~r~)^2^ + (sum f~i~)^2^ ]^1/2^ f~r~ = real part of the scattering factors at theta = 0 f~i~ = imaginary part of the scattering factors at theta = 0 the sum is taken over each atom in the unit cell

May appear in list containing _exptl_crystal_id

The permitted range is 0.0 -> infinity

**Type:** numb

**Category:** exptl_crystal

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