Dear Lammps experts,

I have a problem in stretching of the anatase in tenisle test. Actuallz, I think that as I apply the periodic boundarz conditions in all x,y,z directions I cannot see the stretching of the sample.Neverhterles,I cannot omit the periodic boundary conditions becaue of the type of phase field computation.

Please let me know whether you have any suggestion.

input file

#Phase 1 ------------------------------------------Simulation main setup-------------------------------------------------

dimension 3

units real

atom_style charge

boundary p p p

variable lz0 equal 60

#simulation box

region box block 0 15.144 0 11.358 0.0 70 units box

create_box 2 box #2 is number of atoms

# it was very difficult to finally find these positions

lattice custom 1 a1 3.786 0.00000 0.00000 a2 0.0000 3.786 0.00000 a3 0 0 9.514 &

basis 0.0000 0.2500 0.3750 &

basis 0.0000 0.7500 0.6250 &

basis 0.5000 0.7500 0.8750 &

basis 0.5000 0.2500 0.1250 &

basis 0.0000 0.0000 0.1700 &

basis 0.0000 0.7500 0.4200 &

basis 0.5000 0.2500 0.3300 &

basis 0.5000 0.7500 0.0800 &

basis 0.500 0.5000 0.6700 &

basis 0.500 0.2500 0.9200 &

basis 0.000 0.7500 0.8300 &

basis 0.000 0.2500 0.5800

mass 1 47.86000

mass 2 15.99940

#Phase 2 -------------------------------------------------------tensile model design---------------------------------------------------------

region top_edge block 0 15.144 0 11.358 58 ${lz0} units box

create_atoms 2 region top_edge &

basis 1 1 &

basis 2 1 &

basis 3 1 &

basis 4 1 &

basis 5 2 &

basis 6 2 &

basis 7 2 &

basis 8 2 &

basis 9 2 &

basis 10 2 &

basis 11 2 &

basis 12 2

group top_edge region top_edge

set type 1 charge 2.196

set type 2 charge -1.098

#group model union particle substrate

region middle block 0 15.144 0 11.358 2 58 units box

create_atoms 2 region middle &

basis 1 1 &

basis 2 1 &

basis 3 1 &

basis 4 1 &

basis 5 2 &

basis 6 2 &

basis 7 2 &

basis 8 2 &

basis 9 2 &

basis 10 2 &

basis 11 2 &

basis 12 2

group middle region middle

set type 1 charge 2.196

set type 2 charge -1.098

#group model union particle substrate

region bottom_edge block 0 15.144 0 11.358 0 2 units box

create_atoms 2 region bottom_edge &

basis 1 1 &

basis 2 1 &

basis 3 1 &

basis 4 1 &

basis 5 2 &

basis 6 2 &

basis 7 2 &

basis 8 2 &

basis 9 2 &

basis 10 2 &

basis 11 2 &

basis 12 2

group bottom_edge region bottom_edge

set type 1 charge 2.196

set type 2 charge -1.098

#group model union particle substrate

#Phase 3----------------------------------------Buckingham Potential-----------------------------------------------

pair_style buck/coul/long 15.0

pair_coeff 1 1 717647.40 0.154 121.067

pair_coeff 1 2 391049.10 0.194 290.331

pair_coeff 2 2 271716.30 0.234 696.888

neighbor 2.0 bin # skin distance for real units is by default 2.0

neigh_modify every 1 delay 0 check yes

kspace_style pppm 0.0001

#----Phase 5-------------------------------------Initial Equilibration at 300K: you can apply NVT or NPT----------------------------------------

timestep 1.0 # or 2

velocity all create 300 12345 mom yes rot no

fix 1 middle nvt temp 300.0 300.0 100.0

fix 2 bottom_edge setforce 0.0 0.0 0.0

fix 3 top_edge setforce 0.0 0.0 0.0

thermo 100

run 3000

unfix 1

#----Phase 6---------------------------------------tension phase: NVT and NVE are not allowd because of constant volume during stretching--------------------

variable rate equal 0.01

velocity top_edge ramp vz 0 {rate} z 58 59 sum yes
#fix 4 top_edge move linear 0 0 {rate} units box

#fix 5 middle nve !Achtung! volume is not constant during stretching

fix 6 middle temp/rescale 100 300.0 300.0 10.0 1.0

compute stpa middle stress/atom NULL

compute stgb middle reduce sum c_stpa[3]

variable szz equal c_stgb/vol

thermo 100

thermo_style custom step lx xhi v_szz temp

dump 2 all xyz 100 dump.txt

run 5000