**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^ + f~i~^2^) ]^1/2^ f~r~ = real part of the scattering factors at theta = 0 degree f~i~ = imaginary part of the scattering factors at theta = 0 degree the sum is taken over each atom in the unit cell

**Type:** int

**Mandatory item:** no

The permitted range is [1, infinity)

**Category:** exptl_crystal

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