creating wall with create_atom

Hi I would like to create a wall with create_atom :

region div block 0.0 1.0 -400 400.0 -400 400 units lattice
create_atoms 2 region div units lattice

but I’m getting this error:

Cannot create atoms with undefined lattice

Based on what I have read in document the lattice default is equal 1.0
I don’t know what is my mistake here…
please help me

The default lattice spacing is 1.0, as the doc page

says. But if you want to create_atoms, you have

to define a lattice type (e.g. bcc, fcc), else

the command does not know where to put the atoms.