2D periodicity in lammps

hello everyone

   i am doing 3d simualtion ( 2D periodicity) for tip4p water model by
using following forcefield,

mass 1 1.00794 # H
mass 2 15.9994 # O

pair_style lj/cut/tip4p/long 2 1 1 1 0.15 14.9
pair_modify tail no
kspace_style pppm 1.0e-5
kspace_modify slab 3.0
pair_coeff * * 0.0 0.0
pair_coeff 2 2 0.0 3.1589

bond_style harmonic
bond_coeff 1 0.0 0.9572

angle_style harmonic
angle_coeff 1 0.0 104.52

Please re-read my previous email very carefully. Axel.