On the periodicity of the crystal. We know that it is associated with the lattice constant, or in other words, the distances between the nuclei of the atoms of the element. But another frequency for the conduction electrons follows from this work, it creates the valence electrons or electrons of the atomic core, which is probably localized and are on the boundary of the conduction band.

Why body-iron and copper have a face-centered cubic lattice?

Why body-iron and copper have a face-centered cubic lattice?