LAMMPS Stacking Fault Energy

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Abstract

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This example shows how to run an atomistic simulation to generate the generalized stacking fault (GSF) energy curve for FCC metals. A parallel molecular dynamics code, LAMMPS[1], is used. Excel is used to plot the energy-displacement and Ovito[2] is used to visualize the simulation.

Author(s): Phillip M. Spear

Corresponding Author: Mark A. Tschopp

Input

Description of Simulation

The generalized stacking fault energy curve is obtained by rigidly displacing two halves of a crystal on a (111) plane along a <112> direction in that plane. As the displacement proceeds, the energy of the crystal changes as the atoms slip by each other. The potential used here is the Mishin et al. (1999) aluninum potential. This molecular dynamics simulation first generates a simulation cell with fcc atoms of orient [112] in the x, [-110] in the y, and [-1-11] in the z direction and a total of 6,995 atoms are created. The cell size will be 10 lattice units in the x and y directions and 40 lattice units in the z direction. Note that the units in the x and y direction are modified to reflect the different periodicit boundaries of the structure in the corresponding.The top half of the crystal is shifted in the xy plane along the x direction. With this scheme, the boundary conditions used are periodic, periodic and free surface in the x, y, and z directions, respectively. After the displacement in the x direction is made, the crystal is allowed to relax in the z direction and the energy is calculated and then dumped into the dump.comp.* file.

LAMMPS input script for FCC

This input script was run using the December 21 2011 version of LAMMPS. Changes in some commands in more recent versions may require revision of the input script. To run this script, store it in "in.stack_fault.txt" and then use the "lmp_win_no-mpi.exe < in.stack_fault.txt" in a Windows environment where "lmp_win_no-mpi.exe" refers to the LAMMPS executable.

# Input file for Stack Fault Energy surface of Aluminum
# Phillip Spear, 2012

# ------------------------ INITIALIZATION ----------------------
units 		metal
dimension	3
boundary	p	p	s
atom_style	atomic
variable latparam1 equal 4.05

variable xdim equal ${latparam1}*sqrt(6)/2*10
variable ydim equal ${latparam1}*sqrt(2)/2*10

# ----------------------- ATOM DEFINITION ----------------------
lattice		fcc ${latparam1}
region		1 block 0 ${xdim} 0 ${ydim} 0 20 units box
region		2 block 0 ${xdim} 0 ${ydim} 20 40 units box
region		whole block 0 ${xdim} 0 ${ydim} 0 162 units box
create_box	1 whole
lattice	fcc ${latparam1} orient x 1 1 2 orient y -1 1 0 orient z -1 -1 1
create_atoms	1 region 1
lattice	fcc ${latparam1} orient x 1 1 2 orient y -1 1 0 orient z -1 -1 1
create_atoms	1 region 2


# ----------------------- FORCE FIELDS ------------------------
pair_style	eam/alloy
pair_coeff	* * Al99.eam.alloy Al

# ------------------------- SETTINGS --------------------------
group top region 1
group bot region 2

#######################################
# Displacement
displace_atoms bot move 0.0 0.0 0.0 units box
compute peratom all pe/atom
compute eatoms all reduce sum c_peratom

# Dump to comp  for Ovito post processing 
dump 1 all custom 1 dump.comp.* id type xs ys zs c_peratom fx fy fz

thermo 1
thermo_style custom step pe c_eatoms

#fix 1 all setforce 0 0 NULL

min_style cg
minimize 1e-10 1e-10 1 1


######################################
# SIMULATION DONE
print ${x}
print "All done"

Output

LAMMPS datafile

The following dumpfile in .comp format was also generated during this simulation

Post-Processing

Stacking Fault Energy Curve

Visualization

The simulation can be visualized in AtomEye. To do so, find the name of the first cfg file (Fe_110_sig3_224.cfg, in this case) that results from the simulation and type "~/A Fe_110_sig3_225.cfg" in a UNIX environment, where "~/A" is the location of the AtomEye file. Alt+0 will color the atoms according to pyy. Use insert and delete to scroll through the images to see the fracture.

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Acknowledgments

The authors would like to acknowledge funding for this work through the Department of Energy.

References

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