Input Files

Introduction

To run OpenMKM, two input files are required:

A YAML file that specifies parameters related to the reactor.
An XML/YAML file that specifies thermodynamic and kinetic parameters.

When running OpenMKM in the command line, the following syntax is used:

omkm reactor.yaml thermo.xml

where reactor.yaml and thermo.xml correspond to (1) and (2) above.

These files can be generated manually or by using software, such as pMuTT.

Reactor Input File.

The reactor file, as its extension implies, uses the YAML format, which is a human-friendly data format. This file contains information related to the reactor, such as:

operating conditions,
phases,
composition of gas or surface at initial conditions (t = 0 or z = 0),
solver parameters.

Generating YAML Files

To generate a YAML file, one could:

write it manually,
modify one of OpenMKM’s YAML examples,
use pMuTT’s write_yaml function

This YAML tutorial introduces the YAML-language syntax. Since OpenMKM’s YAML file uses only simple types, readers do not need to write passed the ‘Advanced Options’ heading.

There are several validators available to check your YAML file for syntax errors.This site will show errors and can even reformat your file.

OpenMKM Reactor YAML Format

Quantities with units can be specified in the YAML file as a float or a string. If a float is entered, OpenMKM assumes it is in SI units. If a string is entered, then the units can be explictly specified. For example, the reactor volume could either be specified as:

volume: 20 # Units assumed to be m3

volume: "20 cm3" # Explictly state the volume is in cm3

OpenMKM Reactor Format

Below is an exhaustive list of available options supported by OpenMKM. The level indicates whether this field is nested under another.

1st Level	2nd Level	3rd Level	Type	Required	Description	Default Units
reactor			dictionary	Y	Reactor parameters	-
	reactor_type		string	Y	Type of reactor. Supported options: - 'pfr' (plug flow reactor) - 'pfr_0d' (plug flow reactor modeled as a series of CSTRs) - 'cstr' (continuously stirred tank reactor) - 'batch' (batch reactor)	-
	temperature_mode		string	Y	Thermal mode of operation of the reactor. Supported options: - 'isothermal' (constant temperature) - 'heat' (heat transfer with external heat source or sink) - 'adiabatic' (no heat flow) - 'tpd' (temperature programmed desorption, applicable for CSTR/batch reactors only) - 'tprofile' (preset temperature profile along the PFR length, applicable for PFR only)	-
	pressure_mode		string	Y	Pressure mode of the reactor. Valid only for batch, CSTR or pfr_0d reactor models. Supported options: - 'isobaric' (constant pressure) - 'isochoric' or 'isometric' or 'isovolumetric' (constant volume)	-
	nodes		integer	N	Number of CSTRs to model the PFR. Only applicable if reactor.reactor_type='pfr_0d'	-
	volume		float	N	Volume of reactor	m^3
	temperature		float	Y	Temperature of reactor	K
	Tramp		float	N	Temperature ramp. Only required if reactor.mode='tpd'	K/s
	Tend		float	N	Temperature to end temperature ramp. Only required if mode='tpd'	K
	pressure		float	Y	Pressure of reactor	Pa
	area		float	N	Surface area of reactor. Only applicable if reactor.reactor_type='pfr'	m^2
	length		float	N	Length of the reactor. Only applicable if reactor.reactor_type='pfr'	m
	cat_abyv		float	N	Catalyst surface area to reactor volume ratio. Only required if a surface phase is specified	m^-1
inlet_gas			dictionary	N	Inlet gas properties. Not applicable if reactor.reactor_type = 'batch'
	flow_rate		float	N	Volumetric flow rate of inlet stream. Not required if inlet_gas.residence_time or inlet_gas.mass_flow_rate is specified	m^3/s
	residence_time		float	N	Residence time of reactor. Not required if inlet_gas.flow_rate or inlet_gas.mass_flow_rate is specified	s
	mass_flow_rate		float	N	Mass flow rate of inlet stream. Not required if inlet_gas.residence_time or inlet_gas.flow_rate is specified	kg/s
simulation				N	Simulation options
	end_time		float	N	Reactor simulation time. For continuous reactors, the system is assumed to reach steady state by this time	s
	transient		boolean	N	If True, transient results written to output files. Otherwise, transient files are empty
	stepping		string	N	Type of time stepping for transient operation. Pairs with simulation.step_size. Supported options: - 'logarithmic' - 'regular'	-
	step_size		float	N	Step size. If simulation.stepping = 'logarithmic', represents the ratio between the next step and the current step. If simulation.stepping = 'regular', represents the time between the next step and the current step in units of time. Use 'regular' stepping if reactor.mode='tpr'	s
	init_step		float	N	Initial time step	-
	output_format		string	N	Format for output files. Supported options: - 'csv' - 'dat'	-
	solver		dictionary	N	Solver options
		atol	float	N	Absolute tolerance of solver	-
		rtol	float	N	Relative tolerance of solver	-
	multi_input		dictionary	N	Multiple runs where temperature, pressure, and flow rate can be varied	-
		multi_T	list of float	N	Multiple temperatures of reactor	K
		multi_P	list of float	N	Multiple pressures of reactor	Pa
		multi_flow_rate	list of float	N	Multiple volumetric flow rates	m^3/s
	sensitivity		dictionary	N	Sensitivity analysis options	-
		full	boolean	N	If True, runs sensitivity analysis using the Fisher Information Matrix (FIM)	-
		reactions	list of str	N	IDs of reactions to perform local sensitivity analysis (LSA)	-
		species	list of str	N	Names of species to perform local sensitivity analysis (LSA)
phases				Y	Phase properties	-
	bulk		dictionary	N	Bulk phase properties	-
		name	string	N	Name of bulk phase	-
	gas			N	Gas properties	-
		name	string	N	Name of gas phase	-
		initial_state	string	N	Non-zero initial mole fractions for gas phase. Multiple species should be separated by commas. For example: "H2: 0.4,N2: 0.6"	-
	surfaces		list of dictionaries	N	Surface phase properties. Note that multiple surface can be specified.	-
		name		N	Name of surface phase	-
		initial_state		N	Non-zero initial coverages for surface phase. Multiple species should be separated by commas. For example: "H2: 0.4,N2: 0.6"	-

Sample Reactor YAML file.

inlet_gas:
    flow_rate: "2 cm3/s"
phases:
    bulk:
        name: bulk
    gas:
        initial_state: "CH3CH3:1.0"
        name: gas
    surfaces:
    -   initial_state: "M(S):1.0"
        name: terrace
reactor:
    cat_abyv: "200 /cm"
    mode: "isothermal"
    nodes: 50
    pressure: "1 atm"
    temperature: 973
    type: "pfr_0d"
    volume: "1 cm3"
simulation:
    end_time: "1000 s"
    init_step: 1.0e-10
    output_format: "csv"
    step_size: 10
    stepping: "logarithmic"
    transient: true

OpenMKM ThermoChemistry Data File

The thermochemistry file specifies physical, thermodynamic, and kinetic parameters of:

phases
species
reactions
interactions
BEPs

The thermochemistry file can be of either XML or YAML format. If you are interested in using XML format for thermochemistry data, the XML can be difficult to generate manually so we recommend creating a CTI file, which has a very similar syntax to Python code. CTI files can be converted to an XML file using ctml_writer.py. Note there are some differences between OpenMKM’s ctml_writer.py and the script supplied by Cantera.

NOTE: XML and thereby CTI formats are going to be deprecated and replaced with YAML in ftuure

Alternatively, Chemkin input files can be converted to Cantera format using ck2cti.py.

OpenMKM Thermochemistry data CTI Format

The OpenMKM CTI format is based on Cantera’s CTI format. Their documentation has a lot of useful information about specifying types and the syntax.

Units

Default units for the CTI file can be specified using a units directive. It takes the following parameters:

length
time
quantity
energy – Used for lateral interactions.
act_energy – Used for activation energies and BEP relationships.
pressure
mass

Below, we show a sample units directive.

units(length="m", time="s", quantity="mol", energy="kcal",
      act_energy="kcal/mol", pressure="atm", mass="g")

The complete list of supported units is available here.

If you wish to override the units for a specific quantity, you can use a tuple (note that this is different than the YAML syntax which uses strings). For example, the units directive above specifies quantity="mol" and length="m" but we would like to specify the site density as 1.e15 molecules/cm2. This can be done using:

site_density = (1.e15, "molec/cm2")

Phases

Ideal Gas

The ideal_gas directive models species in the gas phase.

ideal_gas(name="gas",
          elements="H C", # Elements present in species
          species="H2 CH4 CHCH CH2CH2 CH3CH3",  # Gaseous species
          reactions=["0001", "0003 to 0005"]) # Reaction IDs

Stoichiometric Solid

The stoichiometric_solid directive is used to specify a bulk solid phase. This is useful for balancing empty sites.

stoichiometric_solid(name="bulk",
                     elements="Ru", # Elements present in species
                     species="M(B)", # Bulk species
                     density=(12.45, 'g/cm3')) # Ignored property for isothermal

Interactive Interface

The interacting_interface directive is used to specify a catalytic surface. For heterogeneous catalysis, this is the most important phase. It links two phases (usually an ideal_gas to a stoichiometric_solid), contains the surface intermediates, their interactions, reactions, and BEP relationships.

interacting_interface(name="terrace",
                      elements="Ru H C", # Elements present in species
                      species="""M(S) H(S) C(S) CH(S) CH2(S) CH3(S) CH4(S) CC(S)
                                 CCH(S) CCH2(S) CHCH(S) CCH3(S) CHCH2(S)
                                 CHCH3(S) CH2CH2(S) CH2CH3(S) CH3CH3(S) """,
                      phases="gas bulk", # Connected phases
                      site_density=(2.49e-09, 'mol/cm2'), # Site density
                      interactions=["0000 to 0195"], # Lateral interactions on this phase
                      reactions=["0000 to 0004"], # Reactions on this phase
                      beps="C-C C-H") # BEPs associated with reactions on this phase

Species

OpenMKM Each species present in your mechanism should have its thermodynamic properties specified using one of the following:

NASA7 polynomial
NASA9 polynomial
Shomate polynomial

More information can be found on Cantera’s documentation.

NASA7 Polynomial

NASA7 polynomials use 7 coefficients to describe the heat capacity, enthalpy, and entropy of a species. Common species are available in the Burcat database or can be generated using pMuTT’s Nasa class.

\[\frac {Cp} {R} = a_{1} + a_{2} T + a_{3} T^{2} + a_{4} T^{3} + a_{5} T^{4}\] \[\frac {H} {RT} = a_{1} + a_{2} \frac {T} {2} + a_{3} \frac {T^{2}} {3} + a_{4} \frac {T^{3}} {4} + a_{5} \frac {T^{4}} {5} + a_{6} \frac {1} {T}\] \[\frac {S} {R} = a_{1} \ln {T} + a_{2} T + a_{3} \frac {T^{2}} {2} + a_{4} \frac {T^{3}} {3} + a_{5} \frac {T^{4}} {4} + a_{7}\]

species(name="CH4(S)", # Label used to identify the species
        atoms="C:1 H:4", # Atomic composition of species separated with spaces
        size=1, # Number of sites occupied by species. Only needed for surface species
        thermo=(NASA([250.0, 480.0], # This interval is valid between 250 - 480 K
                     [ 6.37200798E+00, -4.66939392E-03,  6.26492184E-06,
                       4.28698448E-08, -5.33259424E-11, -1.23940270E+04,
                      -2.09817174E+01]),
                NASA([480.0, 1500.0], # This interval is valid between 480 - 1500 K
                     [ 3.73282076E+00,  7.75238626E-03,  1.47755181E-06,
                      -3.18500889E-09,  8.84603159E-13, -1.20467882E+04,
                      -9.12054966E+00])))

NASA9 Polynomial

NASA9 polynomials use 9 coefficients to describe the heat capacity, enthalpy, and entropy of a species. Common species are available in the Burcat database or can be generated using pMuTT’s Nasa9 class.

\[\frac {Cp} {R} = a_{1} T^{-2} + a_{2} T^{-1} + a_{3} + a_{4} T + a_{5} T^{2} + a_{6} T^{3} + a_{7} T^{4}\] \[\frac {H} {RT} = -a_{1} \frac {T^{-2}} {2} + a_{2} \frac {ln {T}} {T} + a_{3} + a_{4} \frac {T} {2} + a_{5} \frac {T^{2}} {3} + a_{6} \frac {T^{3}} {4} + a_{7} \frac {T^{4}} {5} + a_{8} \frac {1} {T}\] \[\frac {S} {R} = -a_{1}\frac {T^{-2}} {2} - a_2 \frac {1} {T} + a_{3} \ln {T} + a_{4} T + a_{5} \frac {T^{2}} {2} + a_{6} \frac {T^{3}} {3} + a_{7}\frac {T^{4}} {4} + a_{9}\]

species(name="CH4(S)", # Label used to identify the species
        atoms="C:1 H:4", # Atomic composition of species separated with spaces
        size=1, # Number of sites occupied by species. Only needed for surface species
        thermo=(NASA9([200.0, 1000.0], # This interval is valid between 200 - 1000 K
                      [22103.71497, -381.846182, 6.08273836, -0.00853091441,
                       1.384646189e-05, -9.62579362e-09, 2.519705809e-12,
                       710.846086, -10.76003744]),
                NASA9([1000.0, 6000.0], # This interval is valid between 1000 - 6000 K
                      [587712.406, -2239.249073, 6.06694922, -0.00061396855,
                       1.491806679e-07, -1.923105485e-11, 1.061954386e-15,
                       12832.10415, -15.86640027]),
                NASA9([6000.0, 20000.0], # This interval is valid between 6000 - 20000 K
                      [831013916.0, -642073.354, 202.0264635, -0.03065092046,
                       2.486903333e-06, -9.70595411e-11, 1.437538881e-15,
                       4938707.04, -1672.09974])))

Shomate

Shomate polynomials use 9 coefficients to describe the heat capacity, enthalpy, and entropy of a species. Common species are available in the NIST database or can be generated using pMuTT’s Shomate class.

\[\frac{c_P}{R}=\frac{1}{R}\bigg(A+Bt+Ct^2+Dt^3+\frac{E}{t^2} \bigg)\] \[\frac{H}{RT}=\frac{1}{RT}\bigg(At+B\frac{t^2}{2}+C\frac{t^3}{3} +D\frac{t^4}{4}-\frac{E}{t}+F\bigg)\] \[\frac{S}{R}=\frac{1}{R}\bigg(A\ln(t)+Bt+C\frac{t^2}{2}+D \frac{t^3}{3}-\frac{E}{2t^2}+G\bigg)\]

where $t=\frac{T}{1000}$ in K

species(name="CH4", # Label used to identify the species
        atoms="C:1 H:4", # Atomic composition of species separated with spaces
        size=1, # Number of sites occupied by species. Only needed for surface species
        thermo=Shomate([298, 1300], # This interval is valid between 298 - 1300 K
                       [-7.03029000E-01,  1.08477300E+02, -4.25215700E+01,
                         5.86278800E+00,  6.78565000E-01, -7.68437600E+01,
                         1.58716300E+02]))

Reactions

Cantera (and consequently OpenMKM) support a wide variety of reactions. See Cantera’s documentation to see supported types.

Surface Reactions

For surface chemistry, the surface_reaction directive will be the most common, which uses a modified Arrhenius expression.

\[k = A T^\beta \exp(-\frac {E_a}{RT})\]

where $k$ is the rate constant, $A$ is the pre-exponential factor, $T$ is the temperature, $\beta$ adds explicit temperature dependence to the pre-exponential parameter, $E_a$ is the activation energy, and $R$ is the molar gas constant.

For surface reactions, $A$ is typically calculated using:

\[A^{SR} = \frac {k_B} {h \sigma^{m-1}}\]

where $k_B$ is the Boltzmann constant, $h$ is the Planck’s constant, $\sigma$ is the site density, and $m$ is the number of surface species (including empty sites).

If $A$ is represented this way, we typically replace $E_a$ with the Gibbs energy of activation, $\Delta G^{TS}$, to include entropic effects based on transition state theory.

\[\Delta G^{TS} = \Delta H^{TS} - T \Delta S^{TS}\]

where $\Delta G^{TS}$ is the Gibbs energy of activation, $\Delta H^{TS}$ is the enthalpy of activation, $T$ is the temperature, and $\Delta S^{TS}$ is the entropy of activation.

surface_reaction("CH4(S) + M(S) <=> CH3(S) + H(S) + M(B)", # Reaction string
                 [ 8.36812e+18, 1,  5.55117e+00], # A, beta, and Ea respectively
                 id="0001") # ID referenced by phase BEP directives

Adsorption Reactions

Adsorption reactions also use the surface_reaction directive but with a couple of changes. The stick keyword must be specified and the first parameter represents the sticking coefficient, $s$, instead of the pre-exponential factor, $A$.

\[A^{ads} = \frac {s}{\sigma^{m}}\sqrt \frac{RT}{2\pi M_i}\]

where $A^{ads}$ is the pre-exponential for an adsorption reaction, $s$ is the sticking coefficient, $\sigma$ is the site density, $m$ is the number of surface species including empty sites, $R$ is the molar gas constant, $T$ is the temperature, and $M_i$ is the molecular weight of the gas species.

surface_reaction("CH2CH2 + M(S) <=> CH2CH2(S) + M(B)", # Reaction string
                 stick( 5.00000e-01, 0.0,  3.67653e+00), # Stick keyword indicates adsorption, values are s, beta, and Ea
                 id="0001")

Lateral Interactions

The interactions among adsorbates can cause weaker or tighter binding energies. These are handled in OpenMKM using lateral interactions. Currently, we support piecewise linear interactions.

\[H_{ij} = \omega_{ijk} \theta_{j} + b_{ijk}\]

where $i$ is the species affected by species $j$, $H_{ij}$ is the enthalpic change due the coverage effect, $\theta_{j}$ is the coverage of species $j$, $\omega_{ijk}$ and $b_{ijk}$ are the slope (strength) and intercept of the coverage effect at interval $k$.

They can be specified in two ways using the lateral_interaction directive. Either pairwise or using a matrix.

Pairwise Interactions

lateral_interaction(species="H(S) C(S)", # Species i, Species j
                    coverage_thresholds=[0, 0.11, 1], # Intervals to change 
                    strengths=[0.0, -19.0], # Slope of lateral interaction
                    id="0001")

In the above example, the lateral interaction strength between H(S) and C(S) is 0 between 0 - 0.11 ML of C(S), and -19 kcal/mol (specified using the energy parameter in the units directive) between 0.11 ML - 1 ML of C(S).

Matrix Interactions

The lateral interaction matrix takes the following parameters:

species – species which have lateral interactions
interaction_matrix – a matrix denoting the lateral interaction strengths, and
coverage_thresholds – coverage thresholds above which lateral interactions modify enthalpy of species.

lateral_interactions(
    species = 'N(S1) H(S1) NH3(S1) NH2(S1) NH(S1)',
    interaction_matrix = [[-47.0179, -17.7545, -25.1631, -20.7620, -48.7823],
                          [-17.7545,  -6.7043,  -9.5019,  -7.8400, -18.4208],
                          [-25.1631,  -9.5019, -13.4668, -11.1115, -26.1074],
                          [-20.762,   -7.8400, -11.1115,  -9.1681, -21.5412],
                          [-48.7823, -18.4208, -26.1074, -21.5412, -50.6129]],
    coverage_thresholds = [0, 0, 0, 0, 0])

Bell-Evans-Polanyi (BEP) relationships

Reaction activation energies can be specified using BEP relationships. To specify BEP relationships, use the bep directive, which takes the following:

slope – slope of the BEP linear relationship
intercept – intercept of the BEP relationship
direction – Direction of the BEP. Supported values are cleavage and synthesis.
id – Optional argument to distinguish the BEP relationship. If no value is given, a numerical 4 digit integer starting with 0001 is used to distinguish the BEP relationships
cleavage_reactions – List of associated reaction ids where a bond is broken
synthesis_reactions – List of associated reaction ids where a bond is formed

bep(id='C-H', # Used by phases to identify the BEPs present
    slope=1.02, # Slope
    intercept=(24.44, 'kcal/mol'), # Intercept
    direction='cleavage', # Direction (cleavage or synthesis)
    cleavage_reactions=["0003", "0005", "0007 to 0009", "0013 to 0017"],
    synthesis_reactions=[])

OpenMKM Thermochemistry YAML Format

The YAML format for thermochemistry is based on Cantera’s YAML format. Their documentation has a lot of useful information about specifying types and the syntax.

Units

Default units for the YAML file can be specified using a units mapping at the top level. It takes the following parameters:

length
time
quantity
energy – Used for lateral interactions.
act_energy – Used for activation energies and BEP relationships.
pressure
mass

Below, we show a sample units mapping.

units: {length: m, time: s, quantity: mol, energy: kcal, act_energy: kcal/mol, pressure: atm, mass: g}

The same units mapping can also be written as

units: 
    length: m
    time: s
    quantity: mol
    energy: kcal
    activation-energy: kcal/mol
    pressure: atm
    mass: g

The complete list of supported units is available here.

If you wish to override the units for a specific quantity, you can specify the unit next to the quantity. For example, the units directive above specifies quantity="mol" and length="m" but we would like to specify the site density as 1.e15 molecules/cm2. This can be done using:

site-density: 1.e15 molec/cm^2

Note: In the thermochemistry yaml format, the powers are denoted with ^. So instead of writing cm2 to denote centimeter squared, use cm^2.

Phases

Phases can control transport, kinetic, and thermodynamic properties of the species. Every simulation will require at least one. The comprehensive set of parameters can be found here. A phase definition in general contains a list of elements, species, reactions, and the associated thermodynamic and kinetic models. A surface phase definition can contain BEPs and lateral interactions as well.

A list of phase definitions in the YAML format are specified using phases mapping.

phases: 
- name: phase_name
  elements: [list of elements]
  species: [list of species]
  thermo: thermodynamic model
  state: {initial state}
  kinetics: kinetics model for the phase
  reactions: all or declared-species or none
  interactions: all or declared-species or none
  bep: all or none
- additional phase definition
- additional phase definition

In the above phase definition mapping:

name: Identifier for a phase definition and is required.
elements: List of elements, mandatory.
species: List of species, mandatory.
thermo: Thermodynamic model, mandatory.
- For gas phase, use thermo: ideal-gas.
- For surface phase, use thermo: ideal-surface.
- For surface phase with lateral interactions, use thermo: surface-lateral-interaction.
state: Thermodynamic state specifying temperature and pressure for gas phase. For surface phase tempeature and surface coverages are defined. The state specified here is not used by OpenMKM, but is superceded by the thermodynamic state specified with initial_state keyword in the reactor yaml file.
kinetics: Kinetics model. Mandatory for gas and surface phases.
- For gas phase, must use kinetics: gas.
- For surface phase (with or without lateral interactions), must use kinetics: surface.
- For bulk phase, kinetics can be omitted.
reactions: Keyword denoting the list of reactions. The allowed options are declared-species, all, and none.
- For gas and surface phases, if no reactions are defined, use none .
- For bulk phase, this keyword can be omitted because kinetics is omitted.
bep: Bell-Evans-Polyanni relations are denoted with bep keyword. At present only all or none are supported. The keyword can be omitted if BEP relations are not defined.
interactions: Mapping to specify the lateral interactions associated with the species that are part of the phase definition. If interactions are not part of phase definition, the keyword can be omitted. If used, allowed options are all, declared-species, and none.

Below we show the most common phases used for heterogeneous catalysis.

phases:
    #===========================================
    # Ideal gas phase definition
    #-------------------------------------------
    - name: gas 
      elements: [H, N, Ar] 
      species: [N2, NH3, H2, Ar] 
      thermo: ideal-gas
      state: {T: 300.0 K, P: 1.01325e+05 bar}
      kinetics: gas 
      reactions: none
    #===========================================
    # Bulk phase (Stoichiometric Solid) definition
    #-------------------------------------------
    - name: bulk
      elements: [Ru]
      species: [RU(B)]
      thermo: fixed-stoichiometry
      state: {T: 300.0 K, P: 1.01325e+05 bar}
    #============================================
    # Simple surface phase definition 
    #-------------------------------------------
    - name: terrace
      elements: [H, Ru, N]
      species: [N2(T), N(T), H(T), NH3(T), NH2(T), NH(T), RU(T)]
      thermo: ideal-surface
      site-density: 2.1671e-09 mol/cm^2
      kinetics: surface
      reactions: declared-species
      state: {T: 300.0 K, coverages: {RU(T): 1.0}}
    #==============================================
    # Surface phase with lateral interactions and BEPs
    #-------------------------------------------
    - name: step
      elements: [H, Ru, N]
      species: [N2(S), N(S), H(S), NH3(S), NH2(S), NH(S), RU(S)]
      thermo: surface-lateral-interaction
      site-density: 4.4385e-10 mol/cm^2
      interactions: declared-species
      kinetics: surface
      reactions: declared-species
      bep: all 
      state: {T: 300.0 K, coverages: {RU(S): 1.0}}

Species

Each species present in your mechanism should have its thermodynamic properties specified using one of the following:

NASA7 polynomial
NASA9 polynomial
Shomate polynomial

More information can be found on Cantera’s documentation.

Below we show the three specie models.

species:
#==========================================================
# NASA7
#---------------------------------------------------------
 - name: CH4(S) # Label used to identify the species
   composition: {C: 1, H: 4} # Atomic composition of species 
   size: 1 # Number of sites occupied by species. Only needed for surface species
   thermo:  
      model: NASA7
      temperature-ranges: [250.0, 480.0, 1500.0]
      data: 
      - [6.37200798E+00, -4.66939392E-03,  6.26492184E-06, 4.28698448E-08, 
         -5.33259424E-11, -1.23940270E+04, -2.09817174E+01]
      - [3.73282076E+00,  7.75238626E-03,  1.47755181E-06, -3.18500889E-09, 
         8.84603159E-13, -1.20467882E+04, -9.12054966E+00]

#==========================================================
# NASA9
#---------------------------------------------------------
 - name: CH4(S) # Label used to identify the species
   composition: {C: 1, H: 4} # Atomic composition of species 
   size: 1 # Number of sites occupied by species. Only needed for surface species
   thermo:
      model: NASA9
      temperature-ranges: [200.0, 1000.0, 6000.0, 20000.0]
      data: 
      - [22103.71497, -381.846182, 6.08273836, -0.00853091441,
         1.384646189e-05, -9.62579362e-09, 2.519705809e-12,
         710.846086, -10.76003744]
      - [587712.406, -2239.249073, 6.06694922, -0.00061396855,
         1.491806679e-07, -1.923105485e-11, 1.061954386e-15,
         12832.10415, -15.86640027]
      - [831013916.0, -642073.354, 202.0264635, -0.03065092046,
         2.486903333e-06, -9.70595411e-11, 1.437538881e-15,
         4938707.04, -1672.09974])))

#==========================================================
# Shomate
#---------------------------------------------------------
 - name: CH4(S) # Label used to identify the species
   composition: {C: 1, H: 4} # Atomic composition of species 
   size: 1 # Number of sites occupied by species. Only needed for surface species
   thermo:
      model: Shomate
      temperature-ranges: [298, 1300] 
      data: 
      - [-7.03029000E-01,  1.08477300E+02, -4.25215700E+01,
         5.86278800E+00,  6.78565000E-01, -7.68437600E+01,
         1.58716300E+02]

Reactions

Cantera (and consequently OpenMKM) support a wide variety of reactions. See Cantera’s documentation to see supported types. In YAML format, the reactions are specified under reactions keyword.

Below are the popular reaction models such as surface and adsorption reactions.

reactions:
#================================================================
# Surface Reaction
#----------------------------------------------------------------
  - equation: CH4(S) + M(S) <=> CH3(S) + H(S) + M(B) # Reaction string
    rate-constant: {A: 8.36812e+18, b: 1, Ea: 5.55117e+00}
    id: "r0001"       # ID referenced by phase BEP directives

#================================================================
# Adsorption Reaction
#----------------------------------------------------------------
  - equation: CH2CH2 + M(S) <=> CH2CH2(S) + M(B)
    sticking-coefficient: {A: 5.00000e-01, b: 0.0, Ea: 3.67653e+00} # rate constant specified with sticking-coefficient
    sticking-species: CH2CH2
    Motz-Wise: true
    id: "r0002"

Lateral Interactions

Pairwise lateral interactions can be defined under under interactions keyword. Below is an example defintion for lateral interaction .

interactions:
    - species:[H(S), C(S)] # Species i, Species j
      strength: [0.0 kcal/mol, -19.0 kcal/mol] # Slope of lateral interaction
      coverage-threshold: [0, 0.11, 1] # Intervals to change 
      id: "i001")

In the above example, the lateral interaction strength between H(S) and C(S) is 0 between 0 - 0.11 ML of C(S), and -19 kcal/mol (specified explicitly).

Bell-Evans-Polanyi (BEP) relationships

Reaction activation energies can be specified using BEP relationships. To specify BEP relationships, use the bep directive, which takes the following:

slope – slope of the BEP linear relationship
intercept – intercept of the BEP relationship
direction – Direction of the BEP. Supported values are cleavage and synthesis.
id – Optional argument to distinguish the BEP relationship. If no value is given, a numerical 4 digit integer starting with 0001 is used to distinguish the BEP relationships
cleavage-reactions – List of associated reaction ids where a bond is broken
synthesis-reactions – List of associated reaction ids where a bond is formed

bep: 
    - id: C-H                   # Used by phases to identify the BEPs present
      slope: 1.02               # Slope
      intercept: 24.44 kcal/mol # Intercept
      direction: cleavage       # Direction (cleavage or synthesis)
      cleavage-reactions: [r0003, r0005, r0007, r0009, r0008, r0013, r0014, r0015, r0016, r0017]
      # No synthesis reactions

Chemkin Users

Use the conversion script, \<CANTERA\_ROOT\>/interfaces/cython/cantera/ck2cti.py, which parses gas.inp, surf.inp and thermdat files to convert Chemkin files into the Cantera CTI input format. For more information, refer to Cantera documentation on input file format.

The Chemkin input files are not sometimes parsed by ck2cti.py script due to the bulk phase definition in surf.inp. Remove the bulk phase definition and retry. If it works, add the missing bulk phase definition directly into the CTI file using the stoichiometric_solid keyword (see section above).