[lammps-users] Box size


I'm little confused about setting size of modeling box and number of
particles in it.

units real
dimension 2
atom_style atomic
boundary p p p

lattice sq 7.5
region box block 0 1000 0 200 -0.005 0.005

As I understand this parameters means, that
lattice spacing is 7.5 Angstroms (unit cell is a cube with size 7.5x7.5x7.5)

box block will be X x Y x Z = (0; 7500)x(0; 1500)x(-0.0375; 0.0375) Angstroms

Is that correct?

And what will be a number of particles?

You are correct for the box. To add atoms you need
to use the create_atoms command.