Friedel pair

The reflections with reciprocal indices $\mathbf{h}$ and $-\mathbf{h}$. Their amplitudes are complex conjugates for a real scattering density, but anomalous scattering can make their intensities unequal.

For real atomic scattering factors, $F(-\mathbf{h})=F(\mathbf{h}{)}^{\ast }$ and $I(-\mathbf{h})=I(\mathbf{h})$.