basis vectors!

Hello!
I am trying to usE the lattice command in Lammps to set up the CaCl2 (C35) Structure. The lattice cammand in Lammps with style custom seems appropriate but when the basis vectors (Cl) in CaCl2 have x,y,z <0 , Do I have to create these atoms with style *single?*any advice?
Thanks,
Fateme

If you add 1 to an x,y,z value < 0, then it's the same
location, since it's an infinite lattice.

Steve

Thank you so much Steve! It helped a great deal:)
F.