Beam bending

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1

Hi,
I am trying to fix one end of a beam and then apply a load on the other end (Cantilever). I have a problem that whenever i run equlibration, the temp never goes to 300! Also in the deformation I have the same problem.
Is there a possibility to use S S S ?
I attached the equlibration script. Thanks

units metal
dimension 3
boundary s s p
atom_style atomic

----------------------- ATOM DEFINITION ----------------------------

variable latparam equal 5.431
variable L_x equal 50
variable L_y equal 10
variable L_z equal 10

lattice diamond {latparam} region whole block 0 {L_x} 0 {L_y} 0 {L_z}
create_box 1 whole

region Si_fixed block 0 {L_y} 0 {L_y} 0 {L_z} units box region Si_middle block {L_y} 40 0 {L_y} 0 {L_z} units box
region Si_load block 40 {L_x} 0 {L_y} 0 ${L_z} units box
region Si_total union 3 Si_fixed Si_middle Si_load

lattice diamond ${latparam} orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
create_atoms 1 region Si_total

------------------------ FORCE FIELDS ------------------------------

pair_style meam
pair_coeff * * library.meam Si Ni.meam Si

neighbor 2.0 bin
neigh_modify delay 0 every 1 check yes

------------------------- SETTINGS ---------------------------------

compute csym all centro/atom 4
compute eng all pe/atom

------------------------- GROUPS ---------------------------------

group Gr_Si_fixed region Si_fixed
group Gr_Si_middle region Si_middle
group Gr_Si_load region Si_load
group Gr_Si_mobile union Gr_Si_load Gr_Si_middle
group Gr_Si_total region Si_total

------------------------------Equilibration---------------------

EQUILIBRATION

reset_timestep 0
timestep 0.001
velocity Gr_Si_mobile create 300 12345 mom yes rot no
fix 1 Gr_Si_mobile nvt temp 300.0 300.0 0.1

Set thermo output

thermo 1000
thermo_style custom step lx ly lz press pxx pyy pzz pe temp

Run for at least 10 picosecond (assuming 1 fs timestep)

run 30000
unfix 1
undump 1

Mohamed

2

Hi,
I am trying to fix one end of a beam and then apply a load on the other end
(Cantilever). I have a problem that whenever i run equlibration, the temp
never goes to 300! Also in the deformation I have the same problem.

*which* temperature? the one for the total system?
well, it cannot, since you are only thermalizing a subset. you need to
monitor the temperature of that subset.

axel.

3

Thanks Axel, I run also into another problem, that always some of the atom leave the bulk and start to move far away during equilibration and that changes the box shape.
Also the 2nd issue is that the lower part of the beam appear far away on the top of the box (due to periodicity). I believe the second is not a problem because during deformation the beam keeps these atoms intact. I would appreciate any suggestions. Thanks

Mohamed

4

Thanks Axel, I run also into another problem, that always some of the atom
leave the bulk and start to move far away during equilibration and that
changes the box shape.

so you have an unstable starting geometry (e.g. too small, wrong
geometry), didn't relax/minimize it properly or are doing the heating
too drastically or a combination of those.

Also the 2nd issue is that the lower part of the beam appear far away on the
top of the box (due to periodicity). I believe the second is not a problem
because during deformation the beam keeps these atoms intact. I would

i have no idea what you mean by that and that also sounds like a
self-imposed issue. that is best resolved by discussing your
simulations and setup with your adviser or a more experience/senior
colleague. a mailing list is a very poor and inefficient replacement
for that.

axel.