Thanks for the replies Dr.Axel and Saransh.
Regarding the energy minimization concept, i have read the documentation that fix store/force is not invoked during minimization. but as it is seen in the i/p file, nve and npt ensambles are also used in the upper and mobile regions respectively, so that the SHOCK, which will be introduced by appplying the velocity command WITHOUT RAMPING is alleviated i.e allowed to settle in the whole domain. Still the force on upper regions is zero, even before minimization.
I am attaching the whole script, containing just 500 atoms of Al.
units metal
boundary p p p
atom_style atomic
lattice fcc 3.615
region box block 0 5.0 0 5.0 0 5.0
create_box 3 box
create_atoms 1 box
pair_style eam
pair_coeff * * Cu_u3.eam
region lower block INF INF INF 1.0 INF INF
region upper block INF INF 4.0 INF INF INF
group lower region lower
group upper region upper
group boundary union lower upper
group mobile subtract all boundary
###############################################Thermal Equilibration####################################################
velocity mobile create 300.0 5812775 dist uniform
fix 1 all nve
fix 2 boundary setforce 0.0 0.0 0.0
fix 3 mobile temp/rescale 10 300.0 300.0 10.0 1.0
thermo 25
timestep 0.001
run 1000
##########################################Applying shear by Velocity Command###################################
fix 10 boundary nve
fix 11 boundary temp/rescale 10 300.0 300.0 10 1.0
fix 12 mobile nvt temp 300.0 300.0 .01
velocity upper set .00000018075 0 0 units box
fix 14 lower setforce 0 0 0
fix 13 upper store/force
compute stress upper reduce sum f_13[1]
variable strain equal 1e-5
variable shear equal (c_stress/(lxlz))
variable shearstress equal (v_shear160.2)
dump 1 upper custom 100 dump.* id type fx
thermo_style custom step temp pe v_strain v_shearstress
run 1000
minimize 1e-5 1e-5 10000 10000
Thanks for the Replies…!!!
Sagar