Temperature increasing in NPT thermpostat

Hello,

I have a question about the temperature when strain on the simulation box by NPT with temperature 1.0 , however ,the tempterature can not stay at 1.0 instead keeping increasing. Can some one help me on this ?

Am I missing something or am I doing something wrong in the input files? Any help is greatly appreciated.

Many thanks

Alehmn

The input file is :

in.file

dimension 3
boundary p p p
units lj
atom_style molecular
neighbor 0.3 bin
neigh_modify delay 2 every 2 one 20000 page 1000000
special_bonds lj 1.0 1.0 1.0

read_data data.lammps

bond_style harmonic
bond_coeff 1 1000 1.0

angle_style cosine
angle_coeff 1 20.0

pair_style lj/expand 2.50
pair_modify shift yes
pair_coeff 1 1 5.0 1.0 0.0 2.5

group chain type 1

fix 1 all nve/limit 0.01

thermo 5000

timestep 0.005
run 50000
unfix 1

velocity chain create 1.0 733994 dist gaussian
fix 2 all npt temp 1.0 1.0 1000 iso 0 0 100.0 drag 2
thermo_style custom step temp pxx pyy pzz lx ly lz vol press epair ebond eangle etotal
thermo 1000
timestep 0.005
run 3000000
write_restart run1.restart
unfix 2

Uniaxial Tensile Deformation (at a constant volume)

fix 1 all npt temp 1.0 1.0 100 y 0 0 100.0 z 0 0 100.0 drag 2
fix 2 all deform 1 x erate 0.001 units box remap x
timestep 0.005
variable tmp equal “lx”
variable L0 equal ${tmp}
variable tstep equal “step”
variable mytemp equal “temp”
variable strain equal “(lx - v_L0)/v_L0”
variable stress equal “0.5*(pyy + pzz)-pxx”
variable mypxx equal “-pxx”
variable mypyy equal “-pyy”
variable mypzz equal “-pzz”
variable mylx equal “lx”
variable myly equal “ly”
variable mylz equal “lz”