Note that default parameter values do not define a body-centered cubic
lattice. A 3D body-centered rectangular lattice is considered as a
series of horizontal 2D rectangular vector lattices. The arguments dx
and dy define the spacings in the horizontal planes. A 2D rectangular
lattice seen in a given horizontal plane is shift halfway (in both
horizontal directions) in the next plane. The argument dz defines the
distance between consecutive horizontal planes. Therefore in order to
define a (unit) body-centered cubic lattice, one should set dz=0.5.