Hi All.
First of all , i would like to apologise u all for being naive, Specially Mr.Steve, Mr. Carlos, Mr. Axel… I didnt noe the wherezbouts of these all Sir. I am posting my i/p script again, infact complete… 
******To find Critical Resolved Shear Stress for pure Cu with one edge dislocation
I am defining the atom coordinates, and input them to LAMMPS, and performing energy minimization. What i see is that the simulation box is continously increasing in size when i am using fix 1 all box/relax iso 0.0 command, while the atoms seem to be where they are. Can someone help please…??? I am attaching the i/p file.
units metal
boundary p p p
atom_style atomic
lattice fcc 3.615 orient x 1 1 0 orient y -1 1 1 orient z 1 -1 2
###53100 atoms
###1 atom types
###-36 241 xlo xhi
###-55 222 ylo yhi
###-37 71 zlo zhi
read_data data.edgedislocation
pair_style eam
pair_coeff Cu_u3.eam
region lower block INF INF INF -45 INF INF units box
region upper block INF INF 212 INF INF INF units box
region left block INF -26 INF INF INF INF INF units box
region right block 231 INF INF INF INF INF units box
group boundary union lower upper left right
group mobile subtract all boundary
compute 2 all centro/atom fcc
dump 2 all cfg 1000 edge.* id type xs ys zs c_2
thermo 100
thermo_style custom step temp pe etotal press vol atoms lx ly lz
min_style cg
fix 1 all box/relax iso 0.0
fix 2 boundary setforce 0.0 0.0 0.0
minimize 1e-5 1e-5 10000 10000