fix orient/fcc trubles

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1

Dear users,

I am using synthetic driven force to study the GB mobility of a sigma 5 grain boundary at 800K, but in plus of GB migration, I observe a kind of sliding of my simulation cell. How can I fix this problem?

Thank you for your help,

**...**

Zakaria EL OMARI
Ingénieur en mécanique des structures

Doctorant en physique des matériaux LSPM-CNRS

Linkdin: fr.linkedin.com/in/elomarizakaria

2

Fix orient/fcc adds a force normal to the GB plane. Sliding

sounds like motion parallel to the plane. Do your atoms

move (slide) w/out the fix invoked?

Steve

3

Without this fix atoms don’t move. The one reason I found is a problem on xi.vec and chi.vec but I’m not sure.

Zakaria

**...**

Zakaria EL OMARI
Ingénieur en mécanique des structures

Doctorant en physique des matériaux LSPM-CNRS

Linkdin: fr.linkedin.com/in/elomarizakaria

4

Dear users,

I check the xi.vec and chi.vec but I still have my simulation box sliding when I apply a fix orient /fcc. Someone get this problem before ?

Thank you for your help,

PS : Below the input parameters, the xi.vec and the chi.vec
It’s a sigma 5 GB <010> (boundary plan (001))

#------------- GEOMETRY-----------------------------------------------------------
dimension 3
boundary p p s
units metal
atom_style atomic
lattice fcc 3.5706
read_restart restart.atoms2

#------------- POTENTIAL----------------------------------------------------------
pair_style eam
pair_coeff * * Ni_u3.eam

#------------- define groups------------------------------------------------------
region lower block INF INF INF INF -32 -4 units box
region upper block INF INF INF INF 4 32 units box
region bordinf block INF INF INF INF INF -36 units box
region bordsup block INF INF INF INF 36 INF units box

group upper region upper
group lower region lower
group bordsup region bordsup
group bordinf region bordinf
group boundary union upper lower
group mobile subtract all upper lower

------------ SETTINGS and COMPUTES----------------------------------------------

compute cna all cna/atom 4.8
compute csym all centro/atom fcc
compute new3d all temp
compute peratom all stress/atom new3d virial
compute p all reduce sum c_peratom[1] c_peratom[2] c_peratom[3]
variable press equal -(c_p[1]+c_p[2]+c_p[3])/(3*vol)
dump 1 all xyz 500 tst.xyz

#------------- Equilibration------------------------------------------------------
reset_timestep 0
timestep 0.001

thermo 100
thermo_style custom step temp ke pe press

velocity all create 1600 12345
fix 2 all nvt temp 800 800 1

run 10000

unfix 2

fix equi all npt temp 800 800 1 x 0.0 0.0 1000.0 y 0.0 0.0 1000.0

run 10000

#------------- Store final cell length for strain calculations--------------------
variable tmpx equal “lx”
variable L0x equal {tmpx} variable tmpy equal "ly" variable L0y equal {tmpy}
print “Initial Length, L0x: {L0x}" print "Initial Length, L0y: {L0y}”

#------------- DEFORMATION--------------------------------------------------------
fix gb upper orient/fcc 0 0 3.5706 0.025 0.25 0.75 xi.vec chi.vec

#------------- Output strain and stress info to file------------------------------

for units metal, pressure is in [bars] = 100 [kPa] = 1/10000 [GPa]

p2, p3, p4 are in GPa

variable strainx equal “(lx - v_L0x)/v_L0x”
variable strainy equal “(ly - v_L0y)/v_L0y”
variable p1 equal “v_strainx”
variable p2 equal “-pxx/10000”
variable p3 equal “-pyy/10000”
variable p4 equal “-pzz/10000”
variable pm equal “v_p2+v_p3”

#------------- Display thermo-----------------------------------------------------
thermo 100
thermo_style custom step v_p4 v_pm v_p1 temp ke pe press
run 500000

**...**

Zakaria EL OMARI
Ingénieur en mécanique des structures

Doctorant en physique des matériaux LSPM-CNRS

Tél. 06.58.09.57.19
Linkdin: fr.linkedin.com/in/elomarizakaria

chi.vec (173 Bytes)

xi.vec (157 Bytes)

restart.atoms2 (688 KB)

5

Then I don’t know. You might try emailing Stephen Foiles (google him)

at Sandia who has used and further developed this fix.

Steve