Post on 15-Apr-2020
Adri van DuinProfessor in Mechanical Engineering
Director, Materials Computation Center
Dept. of Mechanical and Nuclear Engineering
Dept. of Chemical Engineering
Dept. of Engineering Science and Mechanics
Penn State University, 240 Research East Building
phone: 814-8636277;
E-mail acv13@psu.edu
The ReaxFF method and its applications to atomistic-scale
simulations on atomic-layer deposition and chemical vapor
deposition in complex 2D-materials
2DCC Webinar
Sept 25, 2018
1Work partially funded through NSF award DMR-1539916
mailto:acv13@psu.edu
Current Penn State group members and projects
Postdoctoral staff
Dr. Yun-Kyung Shin Metal alloys, Sulfur-embrittlement, Proteins
Dr. Nadire Nayir 2D-materials
Dr. Weiwei Zhang Fuel cells, proton transfer
Dr. Chen Chen Fuel cells, industry projects
Dr. Dundar Yilmaz Ferroelectrics, polymers
Dr. Malgorzata Kowalik Carbon fibers
Dr. Chowdhury Ashraf Combustion, carbon materials
PhD-students
Jamil Hossain Battery interface simulations
Dooman Akbarian Ferroelectrics, polymerization
Abhishek Jain Atomistic and continuum scale combustion
Seung Ho Hahn Silica based glasses, treibochemistry, leaching
Kate Penrod Electron transfer reactions in water
Behzad Damirchi Carbon materials
Sharmin Shabnam Combustion
Nabankur Dasgupta Polymer hydrolysis,, supercritical water
Mert Sengul Machine learning, cold sintering
Siavash Rajabpour Carbon fibers, chemical vapor deposition
Karthik Ganeshan MXene/water interfaces
2
Outline
- The ReaxFF reactive force field
- Overview of ReaxFF applications
- Applications to MXenes
- Applications to MoS2 CVD growth
- Summary
ReaxFF MD simulation
of S2 gas reacting with a
MoO3 slab at T=1000K
ReaxFF MD simulation of the
indentation of a Ni-slab with a
diamond fragment (Tavazza et al.,
J.Phys.Chem C 2016, 119, 13580ReaxFF MD simulation
of char combustion at
T=2500K
Material Computation Center (MCC) within Penn State
Material Research Institute (MRI)
MCC Four Lab Solution: Theory, Synthesis,
Fabrication, Characterization
Evaluate
material
candidates
Nanofab
Material Characterization Lab
Fabricate
materials
Characterize
materials
- MCC allows
Nanofab/MCL/2DCC to focus
on high-probability materials
- Simulation is relatively
inexpensive – allows testing
of out-of-the-box concepts
2DCC
Synthesize
materials
MCC has responded to over 1500 requests for software and/or parameter sets
through the MCC-website query form – started July 2015.
MCC Software/parameter distribution
Quantum mechanics
(1-1000 atoms)
Empirical force
fields (1-108 atoms)
Grain/Grain
boundaries
Multigrain
Design
Phase field,
CALPHAD
CFD, Finite
element
Length scales in Material Computation
Reactive force fields
Reactive
force fields
-To get a smooth transition from nonbonded to single, double and
triple bonded systems ReaxFF employs a bond length/bond order
relationship [1-3]. Bond orders are updated every iteration.
-All connectivity-dependent interactions (i.e. valence and torsion
angles, H-bond) are made bond-order dependent, ensuring that their
energy contributions disappear upon bond dissociation.
- Nonbonded interactions (van der Waals, Coulomb) are calculated between
every atom pair, irrespective of connectivity. Excessive close-range
nonbonded interactions are avoided by shielding.
- ReaxFF uses EEM, a geometry-dependent charge calculation
scheme that accounts for polarization effects [4].
Key features of ReaxFF
1. Brenner, D. W., (1990) Physical Review B 42, 9458-9471
2. Tersoff, J., (1988) Physical Review Letters 61, 2879-2882.
3. Abell, G. C., (1985) Physical Review B 31.
4. Mortier, W. J., Ghosh, S. K., and Shankar, S. (1986) JACS 108, 4315-4320.
Calculation of bond orders from interatomic distances
Introduction of bond orders
6,
4,
2,
5,
3,
1,
'
exp
exp
exp
bo
bo
bo
p
o
ij
bo
p
o
ij
bo
p
o
ij
boij
r
rp
r
rp
r
rpBO
Sigma bond
Pi bond
Double pi bond
0
1
2
3
1 1.5 2 2.5 3
Interatomic distance (Å)
Bond o
rder
Bond order (uncorrected)
Sigma bond
Pi bond
Double pi bond
6,
4,
2,
5,
3,
1,
'
exp
exp
exp
bo
bo
bo
p
o
ij
bo
p
o
ij
bo
p
o
ij
boij
r
rp
r
rp
r
rpBO
Sigma bond
Pi bond
Double pi bond
6,
4,
2,
5,
3,
1,
'
exp
exp
exp
bo
bo
bo
p
o
ij
bo
p
o
ij
bo
p
o
ij
boij
r
rp
r
rp
r
rpBO
Sigma bond
Pi bond
Double pi bond
0
1
2
3
1 1.5 2 2.5 3
Interatomic distance (Å)
Bond o
rder
Bond order (uncorrected)
Sigma bond
Pi bond
Double pi bond
Reaction barriers for concerted reactions
0
10
20
30
40
50
60
70
Reaction coordinate
En
erg
y (
kca
l/m
ol)
water 2
water 3
water 4
water 5
water 6
0
10
20
30
40
50
60
70
Reaction coordinate
En
erg
y (
kca
l/m
ol)
water 2
water 3
water 4
water 5
water 6
QM ReaxFF
Neutral
ReaxFF barrier for Grob
fragmentation (collaboration with
John Daily, Boulder). QM barrier:
65 kcal/mol (Nimlos et al., JPC-A
2006)
General rules for ReaxFF
- MD-force field; no discontinuities in energy or forces even during
reactions.
- User should not have to pre-define reactive sites or reaction
pathways; potential functions should be able to automatically handle
coordination changes associated with reactions.
- Each element is represented by only 1 atom type in the force field;
force field should be able to determine equilibrium bond lengths,
valence angles etc. from chemical environment.
0.01
0.1
1
10
100
1000
10000
100000
1000000
0 100 200 300 400
ReaxFF
QM (DFT)
Nr. of atoms
Tim
e/ite
ration (
seconds)
ReaxFF Computational expense
x 1000,000
-ReaxFF allows for
reactive MD-simulations
on systems containing
more than 1000 atoms
- ReaxFF is 10-50 times
slower than non-reactive
force fields
- Better scaling than QM-
methods (NlogN for
ReaxFF, N3 (at best) for
QM
- ReaxFF combines covalent, metallic and ionic elements allowing
applications all across the periodic table
- All ReaxFF descriptions use the same potential functions, enabling
application to interfaces between different material types
- Code has been distributed to over 750 research groups
- Parallel ReaxFF (LAMMPS/ReaxFF) available as open-source
- Incorporated into the ADF/BAND graphical user interface
not currently
described by
ReaxFF
Current development status of ReaxFF
ReaxFF transferability
High energy materials
Batteries
2D-materials
Vp = 3 km/s
RDX dissociation channels
(Strachan et al. JCP 2005)Comparison with experiment – shock velocity and carbon
clustering (Strachan et al. PRL 2013; Zhang et al. JPC-A 2009) Void effects on HE-response
(Nomura et al. PRL 2007)
Li-migration around S4(Islam et al. PCCP 2015)
Li-etching of a defected, strained carbon
nanotube (Huang et al APL 2013)
Li-migration in a carbon onion anode
(Raju et al. JCTC 2015)
Stability of various MoS2 defects
(Ostadhossein et al. in progress)
Comparison of c-lattice expansion for MXenes with
DFT and experiment (Osti et al. ACS-AMI 2016)
High-speed collision of a silica
nanoparticle on graphene (Yoon et al,
Carbon 2016)
Applications to catalytic carbon-growth on Ni-surfaces
Development of Ni/hydrocarbon ReaxFF [1]
Integration of force-
biased Monte Carlo [2]
Electric field effects on
CNT-growth [3]
Ar-bombardment
enhanced surface
catalysis[4]
(1) Mueller, J. E.; van Duin, A. C. T.; Goddard, W. A., III.
Journal of Physical Chemistry C 2010, 114, 4939.
(2) Neyts, E. C.; Shibuta, Y.; van Duin, A. C. T.; Bogaerts,
A. ACS Nano 2010, 4, 6665.
(3) Neyts, E. C.; van Duin, A. C. T.; Bogaerts, A. Journal of
the American Chemical Society 2012, 134, 1256.
(4) Neyts, E. C.; Ostrikov, K.; Han, Z. J.; Kumar, S.; van
Duin, A. C. T.; Bogaerts, A. Physical Review Letters 2013,
110, 065501.
Collaborations with Jonathan Mueller (Caltech, currently U.Ulm) and Erik Neyts (U. Antwerp)
(a) Structures of MAX and MXene phases during MXene synthesis1
(b) Accordion-like structure of Ti3C2Tx MXene2
16 of 41
Introduction (5/7)
Next: Effect of cation
MXenesThe novel material for electrodes
1M. Naguib, V. N. Mochalin, M. W. Barsoum, and Y. Gogotsi, Adv. Mater. 26, 992 (2014). 2F. Wang, C. H. Yang, M. Duan, Y. Tang, and J. F. Zhu, Biosens. Bioelectron. 74, 1022 (2015).
M – early transition metal
A – group 13 or 14 metal (e.g. Al)
X – carbon or nitrogen
Introduction to MXenes
Qualitative comparison of properties with carbon-based materials1
17 of 41
Introduction (6/7)
Next: Effect of cation
MXenesQualitative comparison to carbon-only materials
1P. Simon, Y. Gogotsi, and B. Dunn, Science (80-. ). 343, 1210 (2014).
Introduction to MXenes
Experiment
DFT ReaxFF
Applications of ReaxFF to MXenes
Ti/C MXene defect structure formation and evolution
- MXenes defects show ‘cannibalistic’ growth patterns – material moves
away from the defect sites to deposit additional TixCy patterns
2D-MXene reactions with Urea
- ReaxFF simulations explain high activity of Ti/C/OMXene surfaces to urea conversion
– significantly faster than urea conversion in the gas phase or in water.
- Overbury et al. J.Am.Chem. Soc. 2018, published online, DOI: 10.1021/jacs.8b05913
ReaxFF Experiment
MXene conversion to TiO2/graphene during oxidation
- ReaxFF simulations enable us to follow the conversion of MXenes into
thermodynamically more stable graphene/TiO2 materials
- Lotfi, R., Naguib, M., Yilmaz, D., Nanda, J. and van Duin, A.C.T. (2018) Journal of
Materials Chemistry A 6, 12733-12743.
Development and applications to MoS2
Alireza Ostadhossein, Ali Rahnamoun, Peng Zhao, Sulin Zhang, Yuanxi Wang and Vin Crespi
Bending of pristine and vacancy/mismatched MoS2
Ostadhossein, A., Rahnamoun, A., Wang, Y., Zhao, P., Zhang, S., Crespi, V. H., and van Duin, A. C. T., 2015. ReaxFF
Reactive Force-Field Study of Molybdenum Disulfide (MoS2). Journal of Physical Chemistry Letters manuscript in
preparation.
Comparison of ReaxFF and
DFT Vacancy energies for
MoS2
Extension to MoS2/graphene interfaces
Chowdhury Ashraf and Sungwook Hong (currently USC)
MoS2-Graphene project: Binding energy of S on graphene sheet
Graphene with
monovacancies (C196)
C196S8: Nucleation of S8 on
graphene sheet (11.75 ps)
C195S6: CS2 (in circle) leaving the
graphene sheet (112.25 ps)
S Growth on Graphene Sheet with Vacancies
C195S10 (316.75 ps)C195S30 : Largest S cluster (413 ps)
C195S20 (425 ps)C195S14 (922 ps)
MD vs. fbMC/MD • Alternative MD/fbMC provides better crystallinity, compared
to pure MD
25
Pure MD MD/fbMC
top
side
16S8+ 32Mo in 80×80×80 Å3 box
MoS2 crystallite expansion using the fbMC/MD method
with S/Mo atom addition
Simulations were started by running
10000 MD steps and 10000 FBMC
steps after adding one Mo atom and
three S atom (Atom addition
section).
After adding all components, MD
Simulation was run for 500000
iterations. Then FBMC Simulation
was run for 500000 iterations
(Equilibrium section).
Simulations were run at three
temperatures of 800, 1000,1200 K.
Roghayyeh Lotfi
Side view of growth (atom
addition section only)
MoS2 Growth from S/Mo by FBMC/MD method at 1000 K
Top view of growth (atom addition and
equilibrium sections)
Defect Design and Functionalization in 2D-materials
Dundar Yilmaz, Roghayyeh Lotfi, Chowdhury Ashraf, Sungwook Hong and Adri van
Duin, Journal of Physical Chemistry C 2018, 122, 11911
A technique similar to ”Potato Stamp” can be used to create sulfur vacancy
defects on the MoS2 surfaces. Later these defects can be functionalized
with – for example - small epoxy molecules.
4,000 atoms LAMMPS/ReaxFF simulations (4 cores)
a
c
90%
83%
b
500nm5 μm
Synthesis of MoS2 on hBN with full orientation control. (a) Schematic of PVT system. (b) SEM image of triangular MoS2flakes epitaxially grown on mechanically exfoliated hBN, on a Si/SiO2 substrate. A step edge separates two regions, each
with 83% or 90% of the flakes at the same orientation. Inset shows the same image color-coded by orientation. (c) TEM
image of triangular MoS2 flakes grown on freestanding ME-hBN where crystallinity and alignment with the hBN substrate
are verified by the annular dark field (ADF-) STEM image of a Mo-terminated MoS2 edge and the selected area electron
diffraction from the circled area.
MoS2 growth on Boron Nitride (hBN)with Wei Zhang, Yuaxi Wang and Vin Crespi
Pair binding energy (eV)
Heterostack
Frenkel pairs
Adatom in layer 1
Vacancy in layer 2
Pair binding energy (eV)
Among all defect pair binding energies, a Moad+VB complex is the strongest.
Stable defect pairings in neighboring layers of 2D materials are likely
Frenkel pairs – an adatom in one layer binds strongly to a vacancy in
the other layer.
H
BN
Mo on MoS2
2.90Å
Mo on B vacancy in hBN
2.15Å
Mo interstitial
5.05Å
Periodic MoS2 on hBN
Mo
S
B
N
A Mo interstitial atom sandwiched between pristine MoS2 and hBN, with Mo above a boron vacancy, equilibrates to 5.05
Å interlayer spacing, close to the 4.96 Å of pristine MoS2 on pristine hBN. The individual separations of Mo from each of these sheets in isolation also sum to essentially the same value. Thus Mo+VB on hBN can nucleate the growth of an
MoS2 overlayer with no significant deformation of the surrounding ideal bilayer structure.
Angle θ
Triangle centered on:
Energies of finite MoS2 flakes on monolayer h-BN with boron vacancy and Mo interstitial (black) and without (colored, scattered plots).
h1 h2
doped Mo on hollow site
doped Mo on metal site
m1m2
DFT: 12.39kcal/mol
ReaxFF: 10.41kcal/mol
DFT: 0.00kcal/mol
ReaxFF: 0.00kcal/mol
DFT: 20.33kcal/mol
ReaxFF: 7.63kcal/mol
DFT: 0.10kcal/mol
ReaxFF: -2.23kcal/mol
Comparison between DFT and ReaxFF
Simulation strategy:
Simulations temprature:1200 K, Mo:S ratio=1:2
Before adding, simulations were done by
running 10000 MD steps and 10000 fbMC steps
(5 cycles MD/fbMC).
After one Mo and two S atoms adding, 10000
steps of MD simulation and then 10000 steps of
fbMC simulation (5 cycles MD/fbMC).
Note: h-BN with high density of Mo-doping,
high frequency adding Mo/S atoms randomly on
top of h-BN sheet (fix).
MoS2 growth from adding Mo/S by ReaxFF MD/fbMC simulation
Periodic h-BN sheet with Mo(S)-doping
<
DFT shows the right structure is more stable (top view).
※Left two pictures show the final 2D-structure.
※ The key point for the growth is the formation
of Mo-Mo-Mo triangle structure. Once it formed,
the rotation of MoS2 becomes difficult.
MoS2 growth from adding Mo/S by ReaxFF MD/fbMC simulation
1st 2nd
DFT (side view)
Proposed growth process to build a layer of 2D-MoS2 on h-BN in CVD
3-Mo(triangle) 4-Mo atoms 5-Mo 6-Mo 7-Mo
7-Mo relax (hexagon)2D-MoS2 island formed
MoS2 on h-BN with
Mo-doping (top view)
ReaxFF simulation shows Mo/S species are likely to first aggregate around Mo-sites of BN sheet,
and then grow up to get large area 2-dimentional MoS2(without rotation).
expansion
ReaxFF development for W(CO)6/H2Se CVD mixtures
Roghayyeh Lotfi, Yuanxi Wang and Dundar Yilmaz
- Fairly complex chemistry
– not all CO ligands
dissociate directly, first
several Se-groups have
to bind to the metal center
- After H2Se binding, H2release is exothermic –
likely end product
WSe4H2 or similar
species
ReaxFF connection to CFD (Yuan Xuan-group)
CFD Reacting Simulation resultsAbhishek Jain and Yuan Xuan
W(CO)6
5x10-4
0
W(CO)4(Se)2
W(CO)2(SeH)2(Se)2
W(SeH)2(Se)2
4x10-6
0
4x10-6
0
3x10-6
0
- ReaxFF trained CFD can give detailed gas-phase composition predictions,
which can feed back into experimental CVD chamber design and operation
ReaxFF CFD
W(CO)6 in H2Se
Reaction barriers, pre-exponential factorsW(CO)6
W(SeH)2(Se)2
Sample stage
UQ, weights - go beyond DFT?
Experiment
ReaxFF MD/MC
Hyperdynamics
Crystal seeds, grain
structures vs. time
Morphology
recognition
Machine
learning
Long time behavior
DFT
Multi-scale simulation concept for predicting chalcogenide growth
- ReaxFF has proven to be transferable to a wide range of materials
and can handle both complex chemistry and chemical diversity.
Specifically, ReaxFF can describe covalent, metallic and ionic materials
and interactions between these material types.
- The low computational cost of ReaxFF (compared to QM) makes the
method suitable for simulating reaction dynamics for large (>> 1000
atoms) systems (single processor). ReaxFF has now been parallelized,
allowing reactive simulations on >>1000,000 atoms.
: not currently
described by
ReaxFF
Summary
Collaborators:
- Vin Crespi, Sulin Zhang, Susan Sinnott, Yuanxi Wang (Penn State)
- Kimberley Chenoweth, Vyacheslav Bryantsev and Bill Goddard (Caltech)
- Aidan Thompson, Steve Plimpton (Sandia), Ananth Grama (Purdue),
Metin Aktulga (Purdue) (parallel MD)
Funding: - PSU/KISK startup grant #C000032472
- Illinois Coal grant ICCI 10/7B-3
- NSF (TiO2/water, PdO/Ceria, 2DCC)
- NETL/RUA (Fuel catalysis)
- DoE/NETL (Refractory materials)
- AFRL/SBIR (Hydrocarbon cracking)
- AFOSR/MURI (O-resistant materials)
- DoE/EFRC FIRST-center
- Exxon (Software development, catalysis)
- British Royal Society (initial ReaxFF funding)
Acknowledgments
Websites: http://www.engr.psu.edu/adrihttp://www.rxffconsulting.com
Office: 240 Research East
Phone: 814-863-6277
E-mail: acv13@psu.edu
More
information:
Parallel ReaxFF simulation of
hydrocarbon cracking (4800 atoms, 4
processors)
http://www.engr.psu.edu/adri