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Summer Intern Project
Code for Polycrystalline Sample generation for
MD Simulation in Lammps
Submitted by
Pradeep Kalra
(2014MEB1106)
Supervisor
Dr. Dhiraj Kumar Mahajan
Department of Mechanical Engineering

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TABLE OF CONTENTS
Page
TABLE OF CONTENTS 2
INTRODUCTION 3
CHAPTER 2 REVIEW OF PAST WORK 5
CHAPTER 3 FUTURE PLAN OF ACTION 6

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Chapter 1
Introduction
1.1 Motivation for the Study and Problem Statement
Atomistic simulations have now become commonplace in the study of the deformation and
failure of materials. Increase in computing power in recent years has made large-scale
simulations with billions, or even trillions, of atoms a possibility. Most simulations to-date,
however, are still performed with quasi-2D geometries or rather simplistic 3D setups.
Although controlled studies on such well-defined structures are often required to obtain
quantitative information from atomistic simulations, for qualitative studies focusing on e.g.
the identification of mechanisms, researchers would greatly benefit from a methodology
that helps realize more realistic configurations. The ideal scenario would be a one-on-one
reconstruction of experimentally observed structures. To this end, we have created a
code with the following features:
 The method allows for polycrystalline sample generation with any number of grains
shaped in a 3D enclosed volume.
 It also allows us to have a structure which is continuous ie. can be treated as a differential
similar part of million of atoms.

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1.2 Detailed Work Plan
In our work in summers, we proposed to model a polycrystalline Nickel crystal grain
boundaries for better control on their variation. Analysis of a simpler model helps us getting
insights as it is easier to observe. That is why we divided our plan of action into several parts.
We decided we will begin with modelling of a single crystal Nickel. After complete analysis of
single crystal of Nickel, a polycrystalline Nickel crystal was modelled. The boundary conditions
obtained from single nickel crystal were applied to make polycrystalline Nickel model. Then a
parametric study by changing grain boundary sizes to form CSL grain boundaries in these
polycrystalline crystal will be formed.
Thus the complete project is divided into several tasks and now a step by step study leading
to better insights and understanding will be performed.
In summers we made a polycrystalline material for any metal with any number of grains ie
upto step 2.
Varying Grain Boundaries to see its effect
After modelling of Polycrystalline Nickel we will vary size of grain
boundaries in order to produce CSL grain boundary.
Modelling of Polycrystalline Nickel
Using the boundary conditions obtained from single crystal study and to
observe effect of grain boundaries.
Modelling of Single Crystal Nickel
In order to obtain boundary conditions for Polycrystal
Generation

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Chapter 2
Current Progress and Model
Preparation of Polycrystalline Nickel
Using Matlab self prepared codes and NEPER software, the much needed polycrystalline
Nickel structure was generated.
 The solid block generated in LAMMPS was tessellated using NEPER software which is
poly crystal generator and tessellation software.
 NEPER software tessellated the cube randomly in the number of grains user define
and provides the required coordinates of different region.
 Now integrating LAMMPS input file with Matlab code gives us the flexibility to use
the region defined by NEPER software and fill the region.
 The filling of atoms could be done using randomly oriented grains or the user can
define the orientation of grains required.
 Once the filling of grain is done, the LAMMPS input file is generated which gives us
the required poly crystal structure.
 Code for formation of polycrystalline material with 20 grains is shown in Appendix-1
but for building the code it needs a pos file which can be created from my matlab
code which will give co-ordinates of atoms.
(a) (b) (c)
(b)
Visualization of performed simulation using OVITO.
Figure 1 Image showing poly crystal Nickel structure with different number of grains. (a) 1
grain (b) 10 grains (c) 20 grains
(c) Time step 0 (a) Time step 100000

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Chapter 3
Future Plan Of Action
In our further study wewill make a code to get a polycrystalwith different
sizes of grainswhich will benefit study of diffusionsalot.
Figure 2 : CSL Grain boundaries that we will make under lammps after making some changes
in matlab code.
Reference :
https://www.researchgate.net/profile/L_Fonseca/publication/257954378/figure/fig1/AS:30
5311895310365@1449803436606/Left-Atomistic-representation-of-the-CSL-grain
boundary-in-cubic-HfO-2-with.png

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Appendix-1
Code for making single crystal structure Nickel
################################START################################
###########
# Test of EAM potential for Ni polycrystal grain boundary
units metal
dimension 3
boundary p p p
atom_style atomic
read_data pos_4.Ni
# ------------------------ FORCE FIELDS ------------------------------
pair_style eam/alloy
pair_coeff * * potentials/Ni99.eam.alloy Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni
Ni Ni Ni Ni Ni
neigh_modify every 10 delay 0 one 800000000 check yes page 1000000000
# ------------------------- SETTINGS ---------------------------------
compute csym all centro/atom fcc
compute peratom all pe/atom
######################################
# First minimization
reset_timestep 0
thermo 10
thermo_style custom step lx ly lz press pxx pyy pzz pe temp
min_style cg

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minimize 0e-25 0e-25 0000 0000
print "Compilation done"
log logNi_Minimization1.data
write_data data.minimization