Note that the default arguments do not define a face-centered cubic
lattice. A face-centered rectangular lattice is considered as a series
of horizontal quincunx 2D lattices. The arguments d and dx define the
spacings of the horizontal quincunx. The default values of d and dx
yields unit horizontal quincunx lattices. A quincunx lying in a given
horizontal plane is shifted halfway in a single direction into the next
horizontal plane. The argument dz defines the distance separating two
consecutive horizontal planes. The unit face-centered cubic lattice is
obtained with $d=sqrt(2)/2$, $dx=1$ and $dz=0.5$.