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NSF Pan-American Advanced Studies Institutes (PASI) Workshop January 5-16, 2004. Computational Nanotechnology and Molecular Engineering MSC/Caltech: Dr. Mario Blanco and Dr. Mamadou Diallo. First principles Simulations of Nanoscale Materials Technology William A. Goddard III - PowerPoint PPT Presentation
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1GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
First principles Simulations of Nanoscale Materials Technology
William A. Goddard III Charles and Mary Ferkel Professor of
Chemistry, Materials Science, and Applied PhysicsDirector, Materials and Process Simulation Center
California Institute of Technology, Pasadena, California 91125
[http://www.wag.caltech.edu]
NSF Pan-American Advanced Studies Institutes (PASI) Workshop January 5-16, 2004
Computational Nanotechnology and Molecular EngineeringMSC/Caltech: Dr. Mario Blanco and Dr. Mamadou Diallo
2GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Who is Goddard?
Born El Centro, California (in Southern California desert east San Diego) Public schools of El Centro, Delano, Indio, Lodi, Firebaugh, MacFarland, Oildale (Bakersfield), Modesto, Yuma
BS Engineering, UCLA, June, 1960
PhD Engineering Science (Minor physics) Caltech Oct. 1964
Caltech Chemistry Faculty Nov. 1964-2024
108 PhD’s, 550 publications, Member National Academy of Science, Int. Acad. Quantum Molec. Sci.8 patents in protein structure prediction, new polymerization catalysts, semiconducting processing modelingCo-founded 5 companies (all still thriving)
William Goddard PhD (Engr. Sci. 1965,Caltech) advisor: Pol DuwezPol Duwez DSc (1933, Brussels) advisor: Emile Henriot Emile Henriot DSc (Phys, 1912, Sorbonne, Paris) advisor: Marie CurieMarie Curie DSc (1903, Ecole Phys. Chim. Ind, Paris) advisor: Becqeurel
3GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
What is Caltech?
Throop University founded in 1891 (at Green and Fair Oaks, near old town Pasadena). vocational college, high school, grammar school
~1905 George Ellery Hale, Astronomer came to Pasadena to build Mt. Wilson Observatory (because of clear air)
In ~ 1907 changed from to Throop Polytechnic Institute (engineering college)
In ~1910 Throop moved to current site (previously a citrus grove)
~1915 Arthur Amos Noyes came from MIT to start science (chemistry) at Caltech
~1918 Noyes attracted Robert A. Millikan to Caltech
In ~ 1920 changed to California Institute of Technology
In 1920’s Nobel Prizes to Mulliken (Physics), Morgan (Biology)
4GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Caltech Today
Six Divisions:
•Chemistry and Chemical Engineering
•Biology
•Geosciences
•Physics, Math, and Astronomy
•Engineering and Applied Science
•Humanities and Social Science
~1000 undergraduates
~1200 graduate students
~350 faculty
5GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
What is Beckman Institute?
Gift by Arnold and Mabel Beckman
(Arnold got PhD at Caltech, stayed of faculty for 10 years, then started Beckman Instruments)
Construction finished July,1990
Resource Centers in Chemistry and Biology
•Imaging
•Lasers
•Materials
•Synthesis
•Materials and Process Simulation Center (MSC)
6GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
What is Materials and Process Simulation Center? (MSC)
Senior Staff: All involved in nanotechnolgyWilliam A. Goddard III, DirectorBlanco, Director Process Simulations and Industrial TechnologyCagin, Director Mesoscale and Materials Science Technologyvan Duin, Director Force Field and Materials TechnologyVaidehi, Director of Biotechnology and PharmaMeulbroek, Director Software Integration and Databases Oxgaard, Director of Quantum and Catalysis TechnologyDiallo, Manager Molecular Environmental Technology Molinero, Manager of Complex Materials Simulations Willick, Manager of Computer Technology and Networks
Staff: (over 60) Trained in Chem., Phys., Mat. Sci., Appl. Phys., Biol., Envir. Engr., Chem. Eng., Comp. Sci., Elect. Engr.
Excellent team for complex problems
Critical Mass of Expertise in Most areas of Atomistic Theory and Applications to Materials, Chemistry, and Biology
Including QM, FF, MD, MesoDyn, Stat. Mech. Biochem., Catalysis, Ceramics, Polymers, Semicond., Metal Alloys, Nanotechnology, Environmental Technology
7GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Vision of MSC: First Principles Modeling: Base on QMTo predict macroscale from QM use Multiscale Strategy
EOS of different phases, vacancy energy, surface energy
femtosec
time
distance Å nm micron mm meters
MESO
Continuum(FEM)
QM
MD
MD simulations of deformation
Fracture, Plasticity, Creep,Fatigue with application
scales of time-space
ELECTRONS ATOMS GRAINS GRIDS
First principles Force Field
Constitutive relationsmechanisms plastic deformationMesoscale FF (beads)
FF
hours
seconds
microsec
nanosec
picosecBuild fro
m QMFFMD
MesoContinuum
8GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Materials and Process Simulation Center (MSC)
Each student involved with bothdeveloping tools (theory and software) to solve impossible problems (1/2 effort)•using simulation (and experiment) to develop new materials and processes materials (1/2 effort)
Nearly every project has a strong coupling with experimentExperiment stimulates current theory with impossible problemsResults from simulation guide and interpret experimentsExperiment essential to validate theory and simulation
Ultimately, de novo simulation will be at the heart of chemistry, biology, materials science
9GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Theory Essential to solve Grand Challenges in Technology
Materials Science: Nanoscale Technology• Opportunity: Tremendous potential for new functional materials
(artificial machines smaller than cells)• Problems: Synthesis, Characterization, Design• Need Multiscale Modeling: couple time/length scales from
electrons/atoms to manufacturingBiology: Protein Folding: Predict all structures of life• Opportunity Will soon have Genomes for All Life
Now: Over 700,000 genes but only ~10,000 protein structures • Problem: experiment can do only ~ 2000/year ($200 million)• Need: Prediction of Reliable Protein Structure and Function for
1,000,000 proteinsChemistry: Methane (CH4) Activation, Gas to Liquid• Opportunity Enormous reserves of CH4 for energy, chemicals,
and materials, mostly wasted• Problem: no efficient, selective, low temperature catalyst• Need: Predictive Mechanism to predict new catalystsFirst Principles Theory will lead developments of new technologies in 21st Century
10GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
BIOTECHNOLGY: Membrane Proteins (GPCR), non-natural Amino Acids, Pharma (VLS)POLYMERS: PEM (nafion), Dendrimers, Gas diffusion, Surface Tension, BiobasedCATALYSTS: Methane Activation, Selective Oxidation, ElectroCat (O2), Polar OlefinsSEMICONDUCTORS: Dielectric Breakdown, Si/SiO2/Si3N4 interfaces, B diffusionCERAMICS: Ferroelectrics, Zeolites, Exfoliation ClaysMETAL ALLOYS: Glass Formation, Plasticity (dislocations, crack propagation, spall) NANOSYSTEMS: DNA based Machines, Carbon Nanotubes, nanoelectronicsENVIRONMENTAL: Dendrimers for Selective Encapsulation, Humic acidINDUSTRIAL APPLICATIONS (GM-GAPC, ChevronTexaco, GM-R&D, Asahi Kasei, Toray)
Polymers: Gas Diffusion, Surface Tension Modification, Water solubilityPolymerization Catalysts for Polar MonomersCatalysts: CH4 activation, Alkylation phenols, zeolites (Acid sites/templates)Semiconductors: Dielectric Breakdown nanometer oxides, nitrides, B Diffusion in Si Automobile Engines: Wear Inhibitors (iron and aluminum based engines)Oil Pipelines: Inhibitors for Corrosion , Scale, Wax; Hydrates, DemulsifiersOil Fields: Surfactants for low water/oil interface energy, Basin modelsCeramics: Bragg Reflection GratingsCatalysts: ammoxidation of propaneFuel Cells: H2 Storage, Polymer Electrolyte Membranes, Electrocatalysis
Applications Focus at the MSC
11GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
• GM advanced propulsion: Fuel Cells (store H2, membrane, cathode)• Chevron Corporation: CH4 to CH3OH, Alkylation, Wax Inhibition• General Motors - Wear inhibition in Aluminum engines• Seiko-Epson: Dielectric Breakdown in nm oxide films, TED (B/Si)• Asahi Kasei: Ammoxidation Catalysis, polymer properties• Berlex Biopharma: Structures and Function of CCR1 and CCR5 (GPCRs)• Aventis Pharma: Structures and Function of GPCR’s
Stimulation toward solving impossible problemsCollaborations with Industry
Asahi Glass: Fluorinated Polymers and CeramicsAvery-Dennison: Nanocomposites for computer screens Adhesives, CatalysisBP Amoco: Heterogeneous Catalysis (alkanes to chemicals, EO)Dow Chemical: Microstructure copolymers, Catalysis polymerize polar olefinsExxon Corporation: Catalysis (Reforming to obtain High cetane diesel fuel)Hughes Satellites/Raytheon: Carbon Based MEMSHughes Research Labs: Hg Compounds for HgCdTe from MOMBEKellogg: Carbohydrates/sugars (corn flakes) Structures, water contentMMM: Surface Tension and structure of polymersNippon Steel: CO + H2 to CH3OH over metal catalystsOwens-Corning: Fiberglas (coupling of matrix to fiber)Saudi Aramco: Demulsifiers, AsphaltenesEach project (3 Years) supports full time postdoc and part of a senior scientist
12GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Method Developments in MSC Quantum Mechanics • Solvation (Poisson-Boltzmann)• Periodic Systems (Gaussians)• New Functionals DFT (bond
breaking)• Quantum Monte Carlo methods • Time Dependent DFT (optical spectra)Force Fields• Polarizable, Charge Transfer• Describe Chemical Reactions• Describe Phase Transitions• Mixed Metal, Ceramic, PolymerMesoScale Dynamics• Coarse Grained FF• Kinetic Monte Carlo (Gas Diffusion,
Epitaxial Growth)• Hybrid MD and Meso Dynamics• TribologyUtilization: Integrated, Web-based
Molecular Dynamics• Non-Equilibrium Dynamics
– Viscosity, rheology– Thermal Conductivity
• Solvation Forces (continuum Solv)– surface tension, contact angles
• Hybrid QM/MD• Plasticity
– Formation Twins, Dislocations– Crack Initiation
• Interfacial EnergiesProcess Simulation• Vapor-Liquid Equilibria• Reaction Networks
Method Development critical to progressGenerally not supported by US government or industry
13GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Nanotechnology: Experiment and Theory Closing the Gap
• Opportunity: Nanotechnology provides tremendous potential for new functional materials (artificial machines smaller than cells)
• Problems to be solved before commercialization: – Synthesis – Characterization – Design
• In each area there are tremendous experimental challenges.
• In each case the time to solution will be dramatically decreased by the use of
de novo simulations Multiscale Modeling that couples the time and length scales
from electrons and atoms to manufacturing
14GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Nanoelectronics
Many experimental efforts to make nanoscale electronic devices based on molecules sandwiched between conducting surfaces (e.g., Jim Heath/UCLA-Caltech, Charley Lieber/Harvard, Jan Schön/Lucent, Phaedon Avouris/IBM)
This could be most useful. For example a future MEMS-scale device (say 20 microns in size) might have an onboard computer based on nanometer sized elements with built in sensors and logic to respond to local environment without the necessity of communicating to remote computer.
Thus to be useful the nanosized switches need not be as fast as current computer elements (GHz). They could be even as slow as KHz and still be useful.
Unfortunately little is known about the atomic-level structure and properties of these nanoelectronics systems, making difficult the design of improved devices.
15GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Computational Nanoelectronics
Step 1: Use theory to predict the structures and mechanical properties of Nanoelectronics systems
Step 2: Use theory to predict electrical performance from 1st principles.
To predict electrical performance of experimental systems we must develop QM based methods to predict current/voltage (I/V) performance from first principles.
We have been working on this over the last 2 years (with support from an industrial partner). We can now predict I/V both for isolated molecules and for 2-dimensional slabs (still need to make the software faster for routine use).
We are now in the position to design new systems that can be synthesized and tested.
16GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
CBPQT=cyclobis(paraquat-p-phenylene)
DNP=1,5-dioxynaphthalene
[2]Rotaxane
TTF=tetrathiafulvalene;
Stoddart-Heath-Type [2]Rotaxane Molecular Switch
OFFOFF
Weiqiao DengYun Hee JangSeung Soon JangHoon Kim
17GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
11_26C KAN242
Volts-1 0 1
Cu
rren
t
0
+2.5 V -2.5 V
Return
11_26e KAN242
Voltage-2 -1 0 1 2
Cu
rren
t
-0
+2V -2.5V
-2.5V +2V Switch diode orientation at –2.3V
NDR=AcceptorNDR=AcceptorCharging(?)Charging(?)
redox
DD
++
++
DD ++
++s
O
Me
ON
Fraser Stoddart (UCLA) Jim Heath Caltech)
OFF
TTF
Naphthyl
TTF
Naphthyl
Molecular Switch
Napthyl and TTF nearly equally good donors Rotaxane ring binds to TTF > 300KRotaxane binds to napthyl > 250K Assume ring moves when apply external voltage which cause diode to switch.
ON
OFF
18GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
⎥⎥⎥
⎦
⎤
⎢⎢⎢
⎣
⎡==−
22221
21
12111
1
HHH
HHH
HHH
HHS
M
MMMM
M
KS
121 ][ −Σ−Σ−−= MMM HEG
)()( 21+ΓΓ= MM GGTraceET
Electrode 2
∫∞
∞−Δ= dEVEpVET
h
eVI ),(),()(
Transmission function:
Δp(E,V) difference in the Fermi-Dirac occupations between electrodes, 1 and 2
Green’s function:
HMM obtained from ab initio QM calculation:Molecule
Spectrum functions:
Green’s functions for electrodes g1 and g2:Describe as Cluster, slab and surface
Ele
ctro
de 1
][ 111+Σ−Σ=Γ i
MM HgH 1111 =Σ][ 222
+Σ−Σ=Γ i
MM HgH 2222 =Σ
Overlap matrix S
Fock matrix H
Ab initio
Self energy:Formalism due to Mark Ratner
Atomic level simulation of Current/VoltageFinite (non periodic) case
19GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Naphthyl
-5.50
-5.40
-5.30
-5.20
-5.10
-5.00
-4.90
-4.80
-4.70
-4.60
-4.50
1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00Transmission
energy
TTF
Naphthyl
TTF NaphthylHOMO-1 -6.51 -6.36HOMO -5.56 -5.09LUMO -5.00 -4.93LUMO+1 -4.59 -4.85
TTF
ON
OFF
I-V
-1.5
-1
-0.5
0
0.5
1
1.5
-0.4 -0.2 0 0.2 0.4
Voltage (V)
Current (uA)
TTF
Naphthyl
TTF, OFF
Naphthyl, ON
V(e
nerg
y)
I(transmission)
I(cu
rre
nt)
Voltage
H = HM+Σ
Predicted I(transmission) -V(energy)
Not known experimentally which state is on and which is off
20GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Rotaxane on TTF, OFF Rotaxane on Naphthyl, ON
Nearly degenerate, thus strongly coupled.
~metallic
HOMO LUMOHOMO LUMO
Big gap not coupled.~insulating
Switch mechanism: Location of HOMO and LUMO
21GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Next step on Heath-Stoddart molecular devices
O O O S
S
S
S
OOO
O O O
O O OMe
O OMeO
O O OMe
N
N
N
N
Si Si
Ti / Al Ti / Al
+ +
+
+++
++
++
+++ +
+ +
+ +
+ +
+ +
+ +
+ +
+
+
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+
– e–
+ e–
+
The theory has already shown which site blue box sits on in the On/Off statesWe are now determining how the blue box moves: applied voltage or chemical reductant
Get fundamental understanding of how the device is switched.Currently the switching is done using chemical oxidants, reductants (experiments may take minutes) or by applying a voltage stepIt is not known what the limiting speed is or how it depends on the design
–2e–
+2e–
+
2+
– e– + e– – e–+ e–
22GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Research plan: Optimize molecules for devices
Connection between molecule tail and electrode
NN
OO OO
SSSS
NN NNR
R
SSOO SSSSR
R = NO2, CN, COOH, OH etc
Can do computational experiments in hours
Lab experiments sometimes months
-4
-3
-2
-1
0
1
2
3
4
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5
Voltage (V)
Current (uA)
NAP-CN
NAP
TTF-CN
TTF
INAP-CN/INAP = 1.26 Backbone
R = CN:30% increase
23GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Failure of Theory? Bell Labs Molecular Transistor (Schön)
Drain
SiO2
SS SS SSSS
Source
Gate
PURESAM
SAM transistor: Nature (2001) Vol, 413, p. 713Ion/Ioff = 106
Single molecule transistor:Science (2001) Vol 294, p. 2138 Ion/Ioff = 450 at 1:5000 4K temperature
Goals in theoretical Study:• Validate the ability to predict field-effect modulation behavior • Determine the reason for the difference in behavior of these systems•Design new improved systems
SiO2
SS
Source
Gate
Drain
MIXED SAM
SSSS SSSS
Conducting molecules mixed with
insulator molecules
These papers are now in dispute, Results may
have been faked
24GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Shift in Gate voltage can modify MOs near Fermi energy leading to a transistor effect but the maximum effect is only a factor or 20 not the 450 that Schoen reported. Also this value of 20 depends on the optimum placement of the energies of the MOs.
Our work was done in Sept. 2001 and not published since it seemed so inconsistent with experiment.
Since then the experimental results have been withdrawn because of possible fraud.
Thus the theory might be ok.
-6.5
-6
-5.5
-5
-4.5
-4
-3.5
-3
-2.5
-2
0 0.1 0.2 0.3 0.4 0.5
Gate field (V/A)
Energy (eV)
LUMO
HOMO
Under Drain voltage (1V)
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
0 0.05 0.1 0.15 0.2 0.25
Gate Field (V/A)
Drain current (uA)
Molecular orbitals shift under Gate voltage, can shift to fermi energy of electrodes
Predicted field-effect modulation under Gate voltage
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
0.00 0.20 0.40 0.60 0.80 1.00
Drain bias (V)
Drain Current (uA)
0
0.05
0.1
0.15
0.2
0.25
Experiment (Schoen)Field-effect modulation behavior Single molecule transistor
Ion/Ioff = 450
theory
Gate voltage
Drain biasgate field
theory
Ion/Ioff = 20
25GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Z Z Z Z Z
Z Z Z Z Z
Z Z Z Z Z
Z Z Z Z Z
Sir Yes Sir !!
Sir Yes Sir !!
Luo – Collier – Jeppesen – Nielsen – DeIonno – Ho – Perkins – Tseng – Yamamoto – Stoddart – Heath
Best performance Ordered Self Assembled Monolayer
Assumed Could be...
+ + + + + + + +
+ + + + + + + +
+ +
+ +
+ +
+ +
What is the arrangement of Rotaxanes on surface?
26GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Started with half rotaxane 1 (fewer conformations)
• SAM structures at various packing density• Determine How the SAM structure affects
(1) the shuttling motion and(2) the I-V (current-voltage) characteristics
Bryce, et al. Tetrahed. Lett. (2001), 42, 1143Bryce, et al. J. Mater. Chem. (2003) 13, 1
1
SAM of Rotaxane on Au(111)
27GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
X-ray structure vs. average from MD
Density 1.59 1.546 (3 % ) 1.801 1.789 (0.67
% ) (g/cm3) @ 295 K @ 295 K @ 160 K @ 160 K
Cooke, Tetrahed. Lett. (2001)
UBULUY
(TTF PQT2+ 2 PF6)
VOLMEO
(TTF CBPQT4+ 4 PF6 4 CH3CN)
R = 0.094; Philp, JCS, Chem. Commun. (1991)
Validate Force field - Crystal structure
28GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
1/48(64r3)
3.46 nm2/1
1/36(63r3)
2.59
1/27c(93r3)
1.94
1/24c(64r3)
1.73
1/18c(92r3)
1.30
1/12(32r3)
0.86
UncomplexedComplexedlie downTilt around y-axisUp along yUp along x
SAM at various coverages n(1)/n(Au (111) surf)high low
29GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
15
12
48
36
1618
2427
-75
-65
-55
-45
-35
-25
10 15 20 25 30 35 40 45 50
No. of surface Au atoms per 1
BuS only
SAM 1/15 (footage 1.08 nm2/1)
SAM 1/12 (footage 0.86 nm2/1)
Stand up! Ring face (PQT or Ph) parallel to surface: -contact?
Most stable packing coverage of [0.9, 1.3] (nm2/1)
30GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Good -contact between stations
SAM 1/12 (footage 0.86 nm2/2) SAM 1/24 (footage 1.73 nm2/2)
2
Now do full rotaxane 2 (DNP added with ethylene oxide linker)
31GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
need to understand the “shoulder-to-shoulder sticking” versus “-stacking” on the surface.
This Could be better...Ideal, assumed
+ + + + + + + +
+ + + + + + + +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
z
-Stacking arrangement in [2]rotaxane SAM?
32GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
(TTF)(CBPQT)
(PF6)4(DNP)
“CBPQT@TTF”
Only orbitals around EF
(TTF)(DNP)(CBPQT)(PF6)4
“CBPQT@DNP”
Electronic Structure of Model [2]Rotaxane (with shuttle)
HOMO1(DNP)
HOMO(TTF + CBPQT)
LUMO (CBPQT)
LUMO(CBPQT)
HOMO(TTF)
HOMO1(DNP)
• Significant overlap• Shifted to lower
energy• LUMO+1: CBPQT + TTF• LUMO, LUMO+1 Splitting
Ring provides low-lying LUMO’s.Ring stabilizes energy level of nearby station.
33GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
extended configurationBetter tunneling between
aligned HOMOs (each at each station:
folded configurationBetter tunneling between
aligned HOMO (free station) and LUMO (ring):
Need direct contact betweenfree station and CBPQT such asfolding and -contact
Two Plausible, Conformation-Dependent, Tunneling Mechanisms in [2]Rotaxane
35GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Exper. UCLA
Theory: Goddard, Caltech
36GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Manipulate Graphene, Graphite, and Single Walled Carbon Nanotubes
Motivation: Hongjai Dai, J. Am. Chem. Soc. 2001, 123, 3838-3839The experiment provided evidence of 1-PBSE absorption by imaging gold clusters presumably attached to the ester tails of the molecules absorbed on SWNT, but what is really happening?
1-Pyrene Butanoic Acid Succinimidyl Ester
Purpose: Understand the interaction of 1-PBSE with carbon nanotubes and with one another so that we can use non-covalent sidewall functionalization of carbon nanotubes to for molecular electronics and self assembly.
concept
37GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Methods
Step One: Find out how different parts of PBSE interact with one another in free space.
Step Two: Do the same with a PBSE dimer.
Step Four: Examine packed configurations for pyrene and PBSE on graphene and graphite (check this against experimental results if possible).
Step Three: Look at the dynamics of isolated PBSE clusters on graphene and graphite.
Each pyrene covers 50 graphene atoms, each PBSE can cover 24 or 40 atoms.
38GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
More on MethodsStep Six: Put PBSE on (10,10) nanotube and compare the free energies of different packing configurations. Try different nanotube sizes and chiralities.
Validating Tools – Friction: Our tools need to produce the right energy barrier for translation of the absorbed molecules on the graphene surface. We should have the correct stresses for the shearing of graphite.
Validating Tools – Bonding forces: We should have the right shape for our molecules.
Validating Tools – Non-Bond forces: We should produce the correct inter-plane separation in graphite. Our QEq parameters should give the right charges.
39GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Surprises So FarFor isolated PBSE clusters on graphite, both the ester tail and the pyrene part of PBSE like to lay flat.
Van der Waals interaction is responsible for absorption onto graphite, graphene, and nanotube, but there is strong Coulombic interaction between absorbed PBSE’s.
On Graphene, Coulombic interactions between neighboring PBSE’s has led to tighter than expected optimum packing of PBSE. Whereas a single pyrene covered 50 graphene atoms, a single PBSE can cover 24 or 40 graphene atoms. Results on graphite and nanotubes are pending.
Ester tail
Pyrene
PBSE 4x3
PBSE 4x5
40GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
SAM packing on Au(111) from MD simulation Coverage-dependence conformation (-stacking)
(1) Electronic structure of essential components from QM Role of the ring 1: provide low-lying LUMO’s Role of the ring 2: stabilize levels of nearby stations -orbitals dominant around HOMO-LUMO
(Aliphatic linkers and anchors negligible?)
(3) I-V Calculation from periodic QM and Green’s matrix ona. Fully extended (unfolded) formb. Fully folded formc. Fully folded form w/o linker/anchor
Conformation effect on I-V
Thru-bond effect on I-V
Summary nanoelectronics
41GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Application: Ferroelectric Actuators Must understand role of domain walls in mediate switching
Switching gives large strain,
… but energy barrier is extremely high!
E
90° domain wall
Domain walls lower the energy barrierby enabling nucleation and growth
Essential questions: Are domain walls mobile? Do they damage the material?In polycrystals? In thin films?
Experiments in BaTiO3
1
2
0 10,000-10,000
0
1.0
Electric field (V/cm)S
trai
n (%
)
Use MD with ReaxFF
42GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
)||exp()()(
)||exp()()(
2
2
23
23
si
si
si
si
ci
ci
ci
ci
rrQr
rrQrsi
ci
vvv
vvv
−⋅−=
−⋅−=
ηρ
ηρ
η
η
P-QEq Force Field ModelProper description of Electrostatics is critical
Pair-wise Nonbond Terms between all atomsShort range Pauli Repulsion plus Dispersion (EvdW)
Include Electrostatic interactions between all atoms (ECoulomb) •Describe Charges as distributed (Gaussians)
not point charges •Core charge is fixed to the mass of the atom
(total charge +4 for Ti) •Electron or shell charge is allowed to move
wrt the core (atomic polarizability)•This includes Shielding as charges overlap•Allow charge transfer (shell charges not fixed)•Self-consistent charge equilibration
43GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Charge Equilibration (QEq): Environment dependent charges:
Charge Equilibration (QEq) Require that the chemical potential (dE/dQi) be the same at every atomFix core charge, allow valence charge to transfer and to shift center
Electrostatic energy
Atomic self energy
Pairwise electrostatic interaction(Shielded Coulomb) ( ) l
kkir
rErflj
kiij QQQQrE
ij
ijklij
klij ⎟⎠
⎞⎜⎝
⎛ ⋅+
⋅
=ηη
ηη
,,int
Five universal parameters for each element describes charge distribution, polarization
Original Paper: Rappe and Goddard, J. Phys. Chem. 1991
QEq parameters are fitted to reproduce QM charges on molecules and polarizability of atoms
44GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Use simple Morse Form with 3 universal parameters per ij (R0, D0, ):
Same parameters for same pair of atoms in all environmentsDetermine from QM at very close separations
⎭⎬⎫
⎩⎨⎧
−⋅−−=
=∑≠
)]1(2
exp[2)]1(exp[)(
)(
o
ij
o
ij
r
rMS
r
rMSMSij
MSij
ijji
MSij
MS
DrE
rEE
αα
Distance
ener
gy
Pauli Principle and Dispersion Terms
44
45GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Phase transitions in BaTiO3 from MD
Rhomb. Ortho. Tetra. Cubic
Polarizable ReaxFF
46GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Transition Temperature Transition Temperature (K)(K)
46
Transition Temp.
Rhombohedral to Orthorhombic
Orthorhombic to Tetragonal
Tetragonal to Cubic
Experiment 183 278 393
ReaxFF Between 200-300 Between 300-400 Between 400-500
Phase Rhombohedral
Orthorhombic Tetragonal Cubic
Exp.* 8-9 10-11 15-16 0
ReaxFF 8 10 21 0
* Merz, W. J., Phys. Rev. 76, 1221 (1949)
Spontaneous Polarization Spontaneous Polarization ((uC/cm2)
47GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Hysterisis Loop of BaTiO3 at 300K, 25GHz by MD
47
Apply Dz at f=25GHz (T=40ps).T=300K.
Monitor Pz vs. Dz.
o
PDE
ε
vvv −
=
Get Pz vs. Ez.Ec = 0.05 V/A at f=25 GHz.
Dz
(V/A)
Time (ps)
Applied Field (25 GHz)
Applied Field (V/A)
Polarization (C/cm2)
VDP
VPP
EEEOo
vdwel
εε
vvvv⋅
−⋅
++=3
2
Dipole Correction
Electric Displacement Correction
Ec
Pr
48GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
O Vacancy Jump When Applying Strain
48
X-direction strain induces x-site O vacancies (i.e., neighboring Ti’s in x direction) to y or z-sites.
x
z
y
x
z
y
o
O atom
O vacancy site
49GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Effect of O Vacancy on the Hystersis Loop
49
•Introducing O Vacancy reduces both Pr & Ec.
•O Vacancy jumps when domain wall sweeps.
Perfect Crystal without O vacancy
Crystal without 1 O vacancy.O Vacancy jumps when domain wall sweeps.
Supercell: 2x32x2Total Atoms: 640/639
Can look at bipolar case where switch domains from x to y
Ec
Pr
50GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Computational design: Nano-actuator
Nano-assembled structures
•Isolated PVDF chains prefer combination of Trans and Gauch conformations
•Control the packing density by assembling PVDF chains between Si slabs
•when packing density is low structure contains Trans and Gauch conformations
•Can convert to All Trans with an electric field (get large strains, high frequency)
Pt electrodes
Si substrate
PVDF chains
51GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Computational design: nano-actuator
Si (111) surfacePVDF:1/2 coverage
10 monomer long chains
Play movie
52GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Computational design: Nano-actuator
strain
Zero fieldElectric field
Actuation principle
T and G bonds
All trans bonds
Electric field
All trans bonds
53GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Strain-electric field curves
All trans bonds
Electric fieldElectric field
All trans bonds
Zero field
T and G bonds
54GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Strain-polarization field curves
External Electric Field: E(t) = E0 sin(2 t / T)
T = 240 ps ~4 GHzE0 = 0.64 C/m2=~40 MV/m
5 % strain @ 4 GHz
Polarization (C/m2)
stra
in (
%)
ε = Q P2Strain is proportional to square of polarization
Electrostrictive behavior
Obtain from analyze dynamics
55GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Strain-electric field curves
External Electric Field: E(t) = E0 sin(2 t / T)
T = 120 ps ~8 GHzE0 = 0.64 C/m2=64C/cm2
40 MV/m
Double the frequency
56GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Strain-electric field curves
External Electric Field: E(t) = E0 sin(2 t / T)
T = 120 ps ~8 GHzE0 = 0.32 C/m2=32C/cm2
Half the electric field
It does not work
57GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Biosynthetic Strategies for Nanoscale Assemblies
Use CURRENT biosynthetic processes to make elements for functional nanoscale devices. NEED:
• fasteners- nanorope, nanorivets (covalent attachments)
• containers- fill and empty upon change in pH, T permanent disposal• Sensors- detect change in local state• Energy source - nano fuel cell (H2/O2) • Templates- to organize parts into a regular array
Use Multiscale Theory to design and characterize systems
58GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Nadrian Seeman (NYU)DNA Double Crossover – JACS 118 6131 (96), Biochem. 32 3211 (93)Nanomechanical Device – Nature 397 144 (99)
•Borromean Ring DNA – Nature 386 137 (97)•3 Arm Junctions – Nucleic Acid Res. 14 9745 (86)•DNA Cube Topology – Nature 350 631 (91)•DNA Nanotechnology – Ann. Rev. Biophy. Biomed.Structures 27 225 (98)
Demonstated DNA Bionanotechnology Synthesis
59GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Nanodevice based on DNA B-Z motorFig. 13 a & 13 b : The nanomechanical device based on B-Z transition device shownin fig. 1. 13a : before operation 13b is after operation.
Double cross over DX in light blue. Each circle represents a DNA double helix.Dark blue circle has a fluorescent quencherB-Z device shown in red.After B-Z transition - quenchingseveral such motors can be mounted in a 2-D array that could cause circles in light blue to move
Before operation
After operation
Design and experimental synthesis and testing: Ned Seeman NYUTheory: Testing and modify: Goddard CaltechFunding: NSF-NIRT (Mike Roco
60GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Current Projects in Polymers
Nanostructure in Nafion membranes for fuel cells
Mesoscale simulations of polysaccharides
Controlled Assembly of Dendrimers into 3D structures (Percec, U. Penn)
Controlled Recognition Sites using Cored Dendrimers (Zimmermann, U. Illinois)
Properties of PAMAM Dendrimers as a function of generation
New Polymers with Low Surface Tension (3M)
Design of polymer membranes for selective Gas Diffusion (Avery Dennison)
Solvent dependent structures of Dendrimer Assemblies (Frechet Berkeley)
61GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Overview of projects on Fuel Cells
2
(~200m)
~10m ~100mPt, 2nm
Polymer electrolyte
membrane fuel cell (PEMFC)
Performance is not adequate but considerable uncertainly regarding: The mechanism of Cathode catalysis, Transport of proton from anode to electrolyte to cathodeRole of polymer nanostructure and interfacesUse atomistic simulations to explain current system and then improve performance
62GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Nafion: Polymer electrolyte Membrane in Fuel Cells
Nafion used in PEMFC (Polymer Electrolyte Membrane Fuel Cell) due to its high proton conductivity as well as electrochemical and mechanical stability.
Molecular level study of nanostructure and transport in hydrated Nafion using atomistic simulation
Most studies on this system have focused on
1. Structure of Nafion 2. Transport characteristics under the various conditions
(water content, temperature etc)
Motivation for studyNeed to run catalyst at 120C to avoid CO poisoning of catalyst, but nafion operates only <80CNeed to develop new generation of non-water membranes that operate at 120C and also do not freeze at -20CNeed first to understand nafion
63GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
less blocky(DR=1.1)
not phase-separate
Red: hydrophilicGreen: hydrophobicmore blocky
(DR=0.1)
Get phase separation
hydrophilic domain
How is nanostructure affected by monomeric sequence?
Nanophase-segregation
Objective: investigate the effect of
monomeric sequence on the nanophase-separated structure
and on water transport in hydrated Nafion
Results reported for hydrated Nafion (20 wt % water content)
We find that the monomeric sequence affects
Nanophase-segregated structure Heterogeneity of water/Nafion
interfaceDiffusion of waterElectro-osmotic drag coefficient
64GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
ionized D.R.=1.1(20 wt % water)353.15 K
DR (degree of randomness)=1.1DR (degree of randomness)=0.1
ionized D.R.=0.1 (20 wt % water)353.15 K
blocky Nafion has well-developed phase-separated structure: get large hydrophilic channel which percolates and retains bulk-water structure.
80 Å80 Å
Effect of DR on Nanophase-segregation
65GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
q: reciprocal vector between i and j (q=2/)
rij: real space vector between i and j
i: local density contrast at location i
L: length of simulation system
Structure factor, S(q)
We find that for low q, DR=0.1 has larger intensity than the DR=1.1.This implies that DR=0.1 (blocky Nafion) has more phase-segregation than DR=1.1.
Use calculated structure to predict the results of Small-angle scattering experiments.SAXS: electron density contrastSANS: deuteron density contrast
How measure the extent of phase-segregation?
Theory can predict many details about how structure and properties and predicts S(q) Experimental measurement of S(q) not give detailed structureCombining theory and experiment to conclude full detail about structure and properties
blocky
dispersed
66GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Atomistic three-phase interface: Catalyst, electrolyte, gas
PolymerPolymerElectrolyteElectrolyte
Pt CatalystPt Catalyst
GasGasPolymerPolymerelectrolyteelectrolyte
How does the proton get from the membrane to the catalyst and delivered to the O to get H2O? We are using ReaxFF to determine atomistic rates.
To obtain low overpotential (activation barrier) may require optimized electrolyte-catalyst interface
70GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Ultrashallow junction fabrication
Junctiondepth (xj)
gate length (L)
gateelectrode
gate oxide
source draine-
MOSFET device
silicon substrateGreatly decreased gate length (100 nm) requires ultrashallow junctions (30nm)to minimize short channel effects.
xj (nm) 30-80 20-70 15-45 10-30
Year 2001 2004 2007 2010
L (m) (0.18) (0.13) (0.10) (0.07)
71GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
What are the issues?
Requires Better understanding ofRequires Better understanding of • low-energy implantation• transient enhanced dopant diffusion (TED)• defect/dopant clustering
Requires Development of predictive numerical models
Process requirementsProcess requirements• maximize dopant activation• minimize dopant diffusion• attain box-like doping profiles
Annealing (~ 1000 oC)
B+ implantation (< 1 keV)
Si substrate
z
CB
B
B
z
TED
z
CB
72GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Multiscale modeling and simulation
fundamental data
Kinetic Monte Carlo simulations [long time (>1 sec)]
Atomic-scale calculations• density functional theory• tight binding MD• classical MD
explanation/prediction
validation
Experimental data
100
B+
200 300 400 500 600 700Depth, Å
B c
onc
ent
ratio
n, c
m-3
1021
1022
1020
1019
1018
as implanted
after annealing (1-10 sec)
Technological Problem: Transient Enhanced DiffusionLong range tail. Made worse by pronounced shoulderExplanation: Bs-SiI migration + BsB migration
73GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Orange balls = Si atoms green balls = B atoms
[B-B]s [B-B]s
Bs -Bi Bs -Bi
Bs-Bs-I Bs-Bs-I
TS
(a)
(b)
(c)(e)
(d) (f)
(g)
diffusion pathway for a boron-boron pair.
74GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Kinetic Monte Carlo simulation (CB=Csi=1019 cm-3, T=900 K)
Boron
Si interstitial
Si cluster
I2
t=0 secI3 I5
I2
I10
t=10-6 sec
t=10-3 sec
t=1 sec
75GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
1018
1019
1020
1021
0 300200100 400 500 600
Depth, A
Con
cent
ratio
n, c
m-3
1 keV B+ implantation
1000 oC
950 oC
kink formation
concave & shouldering
diffusion profile evolution experimental vs. simulation
76GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Computational Materials Design Facility (CMDF)Funded by DARPA
To integrate these disparate software into a Virtual Test FacilityWe are developing the CMDF (an integrated Materials Design Facility)• ICARUS visualization and GUI environment• Common-Generalized Materials Data Model• External-Plug in Materials Properties Simulation Tools as modules• Driven by Python as scripting Language• Archiving MP simulations in MP Database• Query/Search MP database• Generate and regenerate Materials Properties• Sockets for 3rd party MP application modules
Materials Properties Modeling software spans modeling scales from electrons, to atoms, to mesoatoms(QM, FF, MM/MD/MC, unit processes, analysis)
77GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
First Principles Reactive force fields: strategy
• Describe Chemistry (i.e., reactions) of molecules-Fit QM Bond dissociation curves for breaking every type of bond
(XnA-BYm), (XnA=BYm), (XnA≡BYm)-Fit angle bending and torsional potentials from QM-Fit QM Surfaces for Chemical reactions (uni- and bi-molecular)-Fit Ab initio charges and polarizabilities of molecules
•Pauli Principle: Fit to QM for all coordinations (2,4,6,8,12)•Metals: fcc, hcp, bcc, a15, sc, diamond•Defects (vacancies, dislocations, surfaces)•cover high pressure (to 50% compression or 500GPa)
•Generic: use same parameters for all systems (same O in O3, SiO2, H2CO, HbO2, BaTiO3)
Require that One FF reproduces all the ab-initio data (ReaxFF)
78GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
ReaxFF Electrostatics energy
Three universal parameters for each element:1991 paper : use experimental IP, EA, Ri; ReaxFF get from fitting QM
ci
si
ci
oi
oi qRRJ &,,,?
Keeping: ∑ =i
i Qq
•Self-consistent Charge Equilibration (QEq)•Describe charges as distributed (Gaussian)•Thus charges on adjacent atoms shielded (interactions constant as R0) and include interactions over ALL atoms, even if bonded (no exclusions)•Allow charge transfer (QEq method)
( ) ∑ ∑<
⎟⎠
⎞⎜⎝
⎛ ++=ji i
iiiiijjiiji qJqrqqJqE2
1),,(}{ χ
Electronegativity (IP+EA)/2
Hardness (IP-EA)
interactions atomic
( ) lk
kir
rErflj
kiij QQQQrE
ij
ijklij
klij ⎟⎠
⎞⎜⎝
⎛ ⋅+
⋅
=ηη
ηη
,,int
Jij
rij
1/rij
ri0
+ rj0
I
2
79GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Reactive Force Field - ReaxFF
VdWCoulVal EEEE ++=Valence energy
Electrostatic energy
short distance Pauli Repulsion + long range dispersion(pairwise Morse function)
•Valence Terms (EVal) based on Bond Order: dissociates smoothly• Bond distance Bond order Bond energy•Allow angle, torsion, and inversion terms where needed•Includes resonance (benzene, allyl)•describes forbidden (2s + 2s) and allowed (Diels-Alder) reactions •Atomic Valence Term (sum of Bond Orders gives valency)
•Pair-wise Nonbond Terms between all atoms•Short range Pauli Repulsion plus Dispersion (EvdW)
80GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Applications of ReaxFF
• Decomposition of High Energy (HE) Density Materials (HEDM)• MD simulations of shock decomposition and of cook-off• Reaction Kinetics from MD simulations• Ferroelectric oxides (BaTiO3) domain structure, • Pz/Ez Hysteresis Loop of BaTiO3 at 300K, 25GHz by MD• Catalysts: Pt Fuel cell anode, cathode, CH transformations• Ni catalyzed growth of bucky tubes• MoOx catalysts: catalyzed growth of bucky tubes• Si-SiO2 and Si-SiOxNy interfaces• Metal alloy phase transformations (crystal-amorphous)• Enzyme Proteolysis • Si-Al-Mg oxides: Zeolites, clays, mica, intercolation with
polymers• MoVNbTaTeOx (Mitsubishi) ammoxidation catalysts
GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
QM/ReaxFF interaction: new RDX decomposition pathway discovered by
ReaxFF; validated by QM
-80
-60
-40
-20
0
20
40
60
80
100
Energy (kcal/mol) RDX
RDX'+HONO
RDX''+2HONO
TAZ+3HONO3N2O+3H2CO
LM2+2N2O+
2H2CO MN+2N2O+
2H2CO
MN+LM2+
N2O+H2CO2MN+N2O+
H2CO
3MN2MN+LM2
RDR+
NO2
RDRo+
NO2INT176+
NO2
INT149+
HCN+NO2
MN+MNH+
HCN+NO2
NNONNNONOOOOHONNNNOOOOHHONNNOOONNNO2ONN
O
N
NC
N
O
O
H
O
N
NC
N
O
O
H
+N2O
+N2O+HONO
+N2O+HONO
+N2O+HONO
+N2O+2 HONO
H2C=O+N2O+2 HCN+2 HONO
N N
N
O2N N
NO2
O
ON N
N
O2N N
NO2
O
O
HONO elimination
NO2 dissociation
concertedNew mechanism
QMReaxFF
8 membered ring
New unimolecular reactionInspired by ReaxFF MD simulationMore important than concerted pathway
Concerted, NO2 and HONO-dissociation pathways(part of the original training set)
82GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
QM + ReaxFF opens door to Complex Reactions
• Use QM to Extend and develop the detailed reaction mechanism for reactions of organics, organometallics– Unimolecular and bimolecular reactions
• Extend ReaxFF to fit all possible unimolecular and bimolecular reactions.
• Use ReaxFF in computational experiments to describe fundamental processes as function temperature and pressure including uni-,bi-,ter, -tetra-molecular reactions
• Include defects, finite grain size, binder, plasticizer in these simulations to determine models for their effect on microstructure and performance of materials
ReaxFF references:1: van Duin, A.C.T.; Dasgupta, S.; Lorant, F.; Goddard III, W.A. J. Phys. Chem. A 2001, 105, 9396.2: van Duin, A.C.T.; Strachan, A.; Stewman,S; Zhang, Q.; Goddard III, W.A., J. Phys. Chem. A 2003, 107, 3803.3: Strachan, A.; van Duin, A.C.T.; Chakraborty, D.; Dasgupta, S.;Goddard III, W.A. Phys. Rev. Letters. 2003, 91, 098301. 4. Zhang. Q.; Cagin, T.; van Duin, A.C.T.; Goddard III, W.A. Phys. Rev. B, subm
83GODDARD - MSC/CaltechGODDARD - MSC/Caltech PASI-Caltech 1/5/04PASI-Caltech 1/5/04
Conclusions
Goddard
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