I have created FCC crystal using lammps:
variable xbox equal 6
variable ybox equal 40
variable zbox equal 36
variable a equal ${LATTCONST}
variable dx equal sqrt(6.0)/2.0
variable dy equal sqrt(2.0)/2.0
variable dz equal sqrt(3.0)
variable xlength equal ${xbox}*${dx}*$a
variable ylength equal ${ybox}*${dy}*$a
variable zlength equal ${zbox}*${dz}*$a
variable BottomLo equal 0.0
variable BottomHi equal 2.99*${dz}*$a # >2*r_cutoff
variable TopLo equal (${zbox}-3.01)*${dz}*$a
variable TopHi equal ${zbox}*${dz}*$a
# --------------- general settings ----------------------------------------------------------
dimension 3
boundary p p f
units metal
atom_style atomic
# ---------------------- creating FCC lattice ----------------------------------------------
lattice fcc ${a} orient x 1 1 -2 orient y 1 -1 0 orient z -1 -1 -1 spacing ${dx} ${dy} ${dz} origin 0.0 0.0 0.0
region whole block 0.000000 ${xlength} 0.000000 ${ylength} 0.0 ${zlength} units box
create_box 1 whole
create_atoms 1 whole
# ---------------- EAM potential ----------------------------------------
pair_style eam/alloy
pair_coeff * * FeNiCrCoCu-heafixed.setfl Ni Ni
neighbor 2.0 bin
neigh_modify delay 5
# ----------- Divide the crystal into 3 regions ---------------------------------------
region Fixed block INF INF INF INF INF ${BottomHi} units box
region Mobile block INF INF INF INF ${TopLo} INF units box
group fixedatoms region Fixed
group mobileatoms region Mobile
group sample subtract all fixedatoms mobileatoms
______________________
||___MOBILE ATOMS __||
||_____________________||
||__SAMPLE ATOMS___||
||_____________________||
||____FIXED ATOMS___||
||_____________________||
I want to apply about shear stress on MOBILE ATOMS by using either of 2 conditions (i) constant stress (ii) constant strain conditions
For applying shear with constant shear strain rate, you can use the "fix move" or "fix deform" commands of LAMMPS. Using the "fix move" command, you can move the fixed atoms with a constant velocity (i.e., constant shear strain rate) and as a result, your mobile atoms will move. Using, the "fix deform" command, you can deform the simulation box with a constant velocity (i.e., constant shear strain rate).
For applying shear with constant shear stress, you may be able to use the "fix setforce" command of LAMMPS.
Reviewing the "Shear" example of LAMMPS may also be helpful.
Hope this helps.
Best,
Milad
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