You seem to be confused about what exactly is a hexagonal close-packed (HCP) crystal. This question is not very complicated, but outside the scope of this mailing list. You should do some reading on the subject, or try drawing it yourself. The following is a correct lattice custom command for your HCP crystal:

variable a equal 2.2568
variable b equal $asqrt(3.0)
variable c equal $a1.5682

Not quite. lattice hcp will build a lattice with the ideal c/a ratio = sqrt(8/3). The Be lattice has a c/a ratio that is about 4% smaller. One solution is to follow lattice hcp with something like

change_box all z scale 0.96 remap

But I think an explicit specification of the Be lattice is the better solution, because it is more self-explanatory.