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Introduction toRMG-Py
RMG Study GroupFebruary 2, 2015
⇌RMGWednesday, February 4, 15
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Combustion chemistry is complex
1250 715
0.1
10
Initial temperature (K)
Igni
tion
dela
y (m
s)
900
1
2Wednesday, February 4, 15
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Modern kinetic models are large
1 80
1000
C atoms in largest alkane
Spec
ies
in k
inet
ic m
odel
3Wednesday, February 4, 15
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We want to build predictive kinetic models for any fuel in any conditions.
Use a Reaction Mechanism Generator
facebook.com/rmg.mit
4
rmg.mit.edurmg.coe.neu.edu
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Reaction mechanism generators need to...
1.Represent molecules (and identify duplicates)
2.Create reactions (and then new species)
3.Estimate thermo and kinetic parameters (quickly!)
4.Choose what to include and what to leave out5
CH3+
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1. Represent Molecules:2-dimensional graphs
CH3CH2· C C*
H
H
H H
H
=
6
multiplicity 21 C u0 p0 c0 {2,S} {3,S} {4,S} {5,S}2 C u1 p0 c0 {1,S} {6,S} {7,S}3 H u0 p0 c0 {1,S}4 H u0 p0 c0 {1,S}5 H u0 p0 c0 {1,S}6 H u0 p0 c0 {2,S}7 H u0 p0 c0 {2,S}
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2. Create reactions:Using reaction families
7
• Template for recognizing reactive sites
• Recipe for changing the bonding at the site
• Rules for estimating the rate
R1 R1R2 R2H H*1 *1*2 *2
*3 *3
Recipe:• Break bond {*1, S, *2}• Form bond {*2, S, *3}• Gain radical {*1, 1}• Lose radical {*3, 1}
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3a. Estimate thermo:Using Benson’s group contributions
8
1) C-(C)(H)3
2) C-(C)3(H)
3) C-(Cb)(C)(H)25) Cb-(H)
4) Cb-(C)
1) 2(-10.20)
2) -1.90
3) -4.86
4) 5.51
5) 5(3.30)
: -5.15 kcal/moleStandard enthalpy of isobutylbenzene
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3b: Estimate kinetics:Using rules based on hierarchical trees
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X—H + Y·∙ <—> X·∙ + Y—H
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4. Choose what to include:Rate-based expansion of the model core
10
AB
CD
E
F
AB
CD
E
FG
H
Whether species “E” is brought in depends on rate of formation of species in the core and a user-defined tolerance
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RMG’s rate-based algorithm
11
Determine species n in the “edge” such that Rn > Redge≠n
Rn ≥ Rchar?
ti+1 ≥ Ƭ
N
Y
Add species n to the core:• Identify if a duplicate of an existing species.•Generate thermochemistry for new species•Generate kinetics for new reactions.•Recalculate pressure-dependent reaction networks.
ti = ti+1
N
Y
Output the reaction mechanism
Build reaction mechanism from ‘core’ species while calculating and monitoring the edge species fluxes
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Now more details...
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• How to define species
• Controlling the flux-based expansion algorithm
• Reactor conditions, Tolerance, Pruning
• Controlling how to get parameters
• Seeds, Libraries, Estimates
• Extra features
• Constraints, Pressure dependence, QMTP, Liquid Phase
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Defining Species:Input file syntax
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species(label=‘n-butane’,reactive=True,structure=smiles(“CCCC”),
)species(
label=‘N2’,reactive=False,structure=InChI(“InChI=1/N2/c1-2”),
)
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Defining Species:Chemical Identifiers
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Molecules can be described using different schemes. For example Ethene can be represented as:
C CH
H
H
H
1 2
3
4
5
6
1 C u0 p0 c0 {2,D} {3,S} {4,S}2 C u0 p0 c0 {1,D} {5,S} {6,S}3 H u0 p0 c0 {1,S}4 H u0 p0 c0 {1,S}5 H u0 p0 c0 {2,S}6 H u0 p0 c0 {2,S}
Atom index
ElementUnpaired electrons
Type of bondsCharge
Lone pair electrons
Adjacency ListSMILESC=C
InChI1S/C2H4/c1-2/h1-2H2
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Controlling the flux-based expansion:Reactor conditions
15
simpleReactor(temperature=(1200,‘K’),pressure=(1.0,‘bar’),initialMoleFractions={
‘n-butane’: 0.1,‘N2’: 0.5,
},terminationConversion={
‘n-butane’: 0.5,}terminationTime=(1e-1,‘s’),
)
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Controlling the flux-based expansion:Tolerance and Pruning
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simulator(atol=1e-16,rtol=1e-8,
)
model(toleranceKeepInEdge=0.1,toleranceMoveToCore=0.5,toleranceInterruptSimulation=0.9,maximumEdgeSpecies=100000
)
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Controlling the flux-based expansion:Tolerance and Pruning
17Kehang Han, RMG study group, 7/10/14. http://cheme.scripts.mit.edu/green-group/rmg/Wednesday, February 4, 15
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Controlling how to get parameters:Libraries and Seeds
database(thermoLibraries = [‘GRI-Mech3.0’, ‘DFT_QCI_thermo’],reactionLibraries = [],seedMechanisms = [],kineticsDepositories = [‘training’],kineticsFamilies = [‘!Intro_Disproportionation’, ‘!Substitution_O’],kineticsEstimator = ‘rate rules’,
)
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See http://rmg.mit.edu/database/for other libraries and depositories
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Controlling how to get parameters:Libraries and Seeds
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General RMG Algorithm
EB
DCA
F
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Controlling how to get parameters:Libraries and Seeds
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Reaction library
EB
DCA
F
A B B C H I
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Controlling how to get parameters:Libraries and Seeds
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Seed mechanism
EG
B
DCA
H I
F
A B B C H I
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Extra features:Species Constraints
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generatedSpeciesConstraints(maximumRadicalElectrons = 2,
)
maximum<Element>Atoms (e.g. Carbon, Sulfur)maximumHeavyAtomsmaximumRadicalElectrons
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Extra features:Pressure Dependence
23
E(kJ/mol)
high pressuremoderate pressurelow pressure
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Extra features:Pressure Dependence
24
pressureDependence(method=‘modified strong collision’,maximumGrainSize=(0.5,‘kcal/mol’),minimumNumberOfGrains=250,temperatures=(300,2000,‘K’,8),pressures(0.01,100,‘bar’,5),interpolation=(‘Chebyshev’,6,4),
)
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Extra features:QMTP
25
1) C-(C)(H)3
2) C-(C)3(H)
3) C-(Cb)(C)(H)25) Cb-(H)
4) Cb-(C)
1) 2(-10.20)
2) -1.90
3) -4.86
4) 5.51
5) 5(3.30)
: -5.15 kcal/moleStandard enthalpy of isobutylbenzene
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Extra features:QMTP
26
⇌RMGMolecule
Connectivity3D
Structure
QuantumChemistry
Input file with3D
Structure
MolecularProperties
2.8
1.4
2.9vib
rot
trans
Distance Geometry
Magoon, G. R. & Green, W. H. Comput. Chem. Eng. 52, 35–45 (2012).Wednesday, February 4, 15
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Extra features:QMTP
27
quantumMechanics(software=‘mopac’,method=‘pm3’,fileStore=‘QMfiles’,scratchDirectory=‘QMscratch’,onlyCyclics=True,maxRadicalNumber=0,
)
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Extra features:Liquid Phase
28
liquidReactor(temperature=(500,‘K’),initialConcentrations={
‘octane’: (6.0e-3,‘mol/cm^3’),‘oxygen’: (5.0e-6,‘mol/cm^3’),
},terminationTime=(5,‘s’),
)
solvation(solvent=‘octane’
)
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Final Options
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options(units=‘si’,saveRestartPeriod=(1,‘day’),drawMolecules=False,generatePlots=False,
)
saveConcentrationProfiles=True/False # liquid phase
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Example Input File
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https://github.com/GreenGroup/RMG-Py/blob/master/examples/rmg/1%2C3-hexadiene/input.py
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