poisson ratio for Nickel using EAM

Dear Lammps users,

I am doing a simple test of uniaxial loading on single crystal nickel to measure the poisson ratio for one EAM potential of nickel

I could not get the suggested result of 0.30 from https://sites.google.com/a/gmu.edu/eam-potential-database/Ni.
what I am getting is poisson ratio start from 0.4 and gradually changing with higher tension strain applied.

The way I am doing it is using fix_deform + npt (pressure on directions perpendicular to loading is controlled to be 1 atm), input file is as follows, I appreciate if anyone could give me suggestions how to do it.

units metal
dimension 3
boundary p p p
atom_style atomic

neighbor 2 bin
neigh_modify delay 1

lattice fcc 3.52 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1

region box block -20 20 -20 20 -2.5 2.5

create_box 2 box
create_atoms 1 box
mass 1 58.71
mass 2 58.71

pair_style eam
pair_coeff **/software/lammps/lammps2/potentials/Ni_u3.eam

compute new all temp/deform
velocity all create 300 887723 temp new

compute PE all pe/atom
compute KE all ke/atom
compute stress all stress/atom pair
compute p all pressure new

thermo_style custom step temp pe etotal c_p[1] c_p[2] c_p[3] lx ly lz vol press

fix 1 all npt temp 300 300 1 x 1.01 1.01 5 z 1.01 1.01 5 couple none

timestep 0.001
thermo 200
thermo_modify temp new

dump overall all cfg 5000 all_*.cfg id type xs ys zs id

fix systemminimize all box/relax iso 0 nreset 5 vmax 0.001
minimize 1E-10 1E-10 2000 2000

run 1000

fix deform1 all deform 1 y delta 0 2 remap x

timestep 0.001
run 40000

Maybe Jon Zimmerman has an idea (CCd).