Hi
I am doing tensile test on amorphous thin films. So I have vacuum on both top and bottom (along Z axis) and I am applying the strain along X axis. But when I am straining the material there is increase in length along Z direction also, i.e. Lz also increases and also few atoms shift to the vacuum zone.
Since I am a new user I am not able to upload images or movies. Please look at my script and let me know where I am going wrong.
This is my script
##########################################################################
# Structure Definition
units metal
atom_style atomic
dimension 3
boundary p p s
lattice diamond 5.466
region totalbox block 0.0 6.0 0.0 6.0 0.0 10.0
create_box 1 totalbox
region surface block 0.0 6.0 0.0 6.0 3.33 6.67
create_atoms 1 region surface
mass 1 28.085
# Potential
pair_style tersoff
pair_coeff * * Si.tersoff Si
neighbor 2.0 bin
neigh_modify every 10 delay 0 check yes
timestep 0.001
#Equilibration
compute peratom all pe/atom
timestep 0.001
velocity all create 300 12345 mom yes rot no
fix 1 all nvt temp 300 300 0.1
thermo 1000
thermo_style custom step lx ly lz press pxx pyy pzz pe temp
run 20000
unfix 1
#Tensile Test
variable tmp equal "lx"
variable L0 equal ${tmp}
fix 1 all npt temp 300 300 1 y 0 0 1 z 0 0 1 drag 1
variable srate equal 1.0e10
variable srate1 equal "v_srate / 1.0e12"
fix 2 all deform 1 x erate ${srate1} units box remap x
fix 1 all npt temp 300 300 1 y 0 0 1 drag 1
variable srate equal 1.0e10
variable srate1 equal "v_srate / 1.0e12"
fix 2 all deform 1 x erate ${srate1} units box remap x
variable strain equal "(lx - v_L0)/v_L0"
variable p1 equal "v_strain"
variable p2 equal "-pxx/10000"
variable p3 equal "-pyy/10000"
variable p4 equal "-pzz/10000"
fix def1 all print 100 "${p1} ${p2} ${p3} ${p4}" file amorphous_thinfilm_Si.def1.txt screen no
thermo 100
thermo_style custom step v_strain temp v_p2 v_p3 v_p4 ke pe press etotal vol lx ly lz
run 50000
######################################################################
Please note that you input script seems to be copied incorrectly. There are repeated lines.
You are trying to deform a shrinkwrap dimension. That makes no sense.
If you want to use fix deform to study straining your system, you must have a bulk system with periodic boundaries, otherwise there will be no straining effect since only with periodic boundaries, the atoms will “pull each other”.
For non-periodic systems, you need to edefine a group at each side and either move those atoms with either fix move or use fix setforce NULL NULL 0.0 and velocity set to move them at the desired rate and then force the other atoms to follow and measure their strain.
Thanks…I have corrected my script now.
Regarding your answer about fix setforce or fix move …can you explain bit more in detail. I am new to lammps so not very well-versed with it
There should be plenty of tutorials demonstrating this. Also, there is the documentation. I don’t have the time to be your teacher/trainer/tutor.
You don’t have to be rude. If you can, you can point me to the tutorials. If not fine.
I am just stating a fact. How is this rude?
Impoliteness works both ways, this statement sounds rather entitled. My intention is not to satisfy your immediate desires, but to put you on a path of self-sufficiency and thus help you not only with your current issue but also enable you to solve future problems better (and on your own).
There are pointers on the LAMMPS home page, there is google, there are the mailing list or forum archives. There is a lot you can do on your own before asking here. The fact that you are new does not release you from doing your due diligence. Please see: https://www.lammps.org/guidelines.html
I have tried all these means and only as a last resort I have created an account in this forum.
You need to differentiate between your original post (which was legitimate and for which you received a suitable answer with pointers to what you can do), and your followup. You cannot have done your research on fix move or fix setforce + velocity within a couple hours. So there is a whole lot more that you can look at and dig into. There are many discussions (probably too many) about all kinds of straining simulations in the archives. Those go back to 2005 and contain nearly 100,000 messages.
One more question: how do you know that this is not the correct physical behavior for the straining rate you are using? The extension in z-direction is to be expected due to shrink-wrap boundaries as soon as atoms are expelled from your film.