Face-centred cubic selection rule
= Face-centred cubic selection rule
For equivalent scatterers on the four conventional fcc sites, the centering factor is $1+e^{i\pi(h+k)}+e^{i\pi(h+l)}+e^{i\pi(k+l)}$. It is four when the integer indices are all even or all odd, and zero otherwise. An additional <atomic basis of a crystal> can impose further extinctions. This rule concerns conventional cubic indexing.