tensile deformation of a bulk

Dear lammps users,
I have a problem with simulation of a tensile deformation of a bulk ( boundary p p p). the simulation box is a 3030180 and the method of tensile deformation is below.
but it does not work! I can not find out its problem. please tell me about the mistake in it.

group fix0 region fix0
group fix1 region fix1
fix 1 all nvt temp 300 300 0.01 drag 0.2
fix fix0 fix0 setforce 0.0 0.0 NULL
velocity fix0 set 0.0 0.0 NULL units box
fix fix1 fix1 setforce 0.0 0.0 NULL
velocity fix1 set 0.0 0.0 NULL units box
run 60000

fix down end & tensile up end

variable vtensile equal 0.5
fix fix0 fix0 setforce 0.0 0.0 0.0
velocity fix0 set 0.0 0.0 0.0 units box
fix fix1 fix1 setforce 0.0 0.0 0.0
velocity fix1 set 0.0 0.0 \${vtensile} units box

thanks,

Dear lammps users,
I have a problem with simulation of a tensile deformation of a bulk (
boundary p p p). the simulation box is a 30*30*180 and the method of tensile
deformation is below.
but it does not work! I can not find out its problem. please tell me about
the mistake in it.

group fix0 region fix0
group fix1 region fix1
fix 1 all nvt temp 300 300 0.01 drag 0.2
fix fix0 fix0 setforce 0.0 0.0 NULL
velocity fix0 set 0.0 0.0 NULL units box
fix fix1 fix1 setforce 0.0 0.0 NULL
velocity fix1 set 0.0 0.0 NULL units box

where is the deformation here supposed to come from?

axel.

and what does "it does not work!" mean?
Ask an imprecise question, and you
will get likely not get a useful answer.

Steve

Dear Axel and Steve,
thanks for your attention and sorry for my ambiguous question. I have defined tow groups in each end of the sample(group fix0 & group fix1). The “fix1” group is considered fixed by commands: fix fix0 fix0 setforce 0.0 0.0 0.0 and velocity fix0 set 0.0 0.0 0.0 units box when the “fix1” group is supposed to cause the tensile deformation by commands: fix fix1 fix1 setforce 0.0 0.0 0.0 and velocity fix1 set 0.0 0.0 {vtensile} units box that "{vtensile} " is : variable vtensile equal 0.5. the commands until “run 60” in my previous email belong to the equilibrium stage.
about my problem: during deformation it doen’t deform correctly. I mean lengthening and necking doesn’t happen at all. the sample ( 3030180 p p p boundary) fractures from the “box0” group without any deformation. I would like to know my mistake in the simulation procedure.
hope to be obvious enough.
thank you very much.

Did the atoms at the ends move and not move as you expected?
Which you can verify thru visualization. If they do, then the
atoms in the middle respond as they want to respond. If they
don't respond the way you expect, that doesn't mean it
is a LAMMPS issue.

Steve