# Species¶

The fields of a species entry are:

name

String identifier used for the species. Required.

composition

Mapping that specifies the elemental composition of the species, for example, {C: 1, H: 4}. Required.

thermo

Mapping containing the reference state thermodynamic model specification and parameters. See Species thermo models.

equation-of-state

A mapping or list of mappings. Each mapping contains an equation of state model specification for the species, any parameters for that model, and any parameters for interactions with other species. See Species equation of state models. If this field is absent and a model is required, the ideal-gas model is assumed.

critical-parameters

Mapping containing parameters related to the critical state of a species. Used in models that incorporate “real gas” effects, such as Redlich-Kwong. See Species critical state parameters.

transport

Mapping containing the species transport model specification and parameters. See Species transport models.

sites

The number of sites occupied by a surface or edge species. Default is 1.

Debye-Huckel

## Species thermo models¶

Fields of a species thermo entry used by all models are:

model

String specifying the model to be used. Required. Supported model strings are:

reference-pressure

The reference pressure at which the given thermodynamic properties apply. Defaults to 1 atm.

### NASA 7-coefficient polynomials¶

The polynomial form described here, given for one or two temperature regions. Additional fields of a NASA7 thermo entry are:

temperature-ranges

A list giving the temperature intervals on which the polynomials are valid. For one temperature region, this list contains the minimum and maximum temperatures for the polynomial. For two temperature regions, this list contains the minimum, intermediate, and maximum temperatures.

data

A list with one item per temperature region, where that item is a 7 item list of polynomial coefficients. The temperature regions are arranged in ascending order. Note that this is different from the standard CHEMKIN formulation that uses two temperature regions listed in descending order.

Example:

thermo:
model: NASA7
temperature-ranges: [300.0, 1000.0, 5000.0]
data:
- [3.298677, 0.0014082404, -3.963222e-06, 5.641515e-09,
-2.444854e-12, -1020.8999, 3.950372]
- [2.92664, 0.0014879768, -5.68476e-07, 1.0097038e-10,
-6.753351e-15, -922.7977, 5.980528]


### NASA 9-coefficient polynomials¶

The polynomial form described here, given for any number of temperature regions. Additional fields of a NASA9 thermo entry are:

temperature-ranges

A list giving the temperature intervals on which the polynomials are valid. This list contains the minimum temperature, the intermediate temperatures between each set pair of regions, and the maximum temperature.

data

A list with one item per temperature region, where that item is a 9 item list of polynomial coefficients. The temperature regions are arranged in ascending order.

Example:

thermo:
model: NASA9
temperature-ranges: [200.00, 1000.00, 6000.0, 20000]
reference-pressure: 1 bar
data:
- [2.210371497E+04, -3.818461820E+02, 6.082738360E+00, -8.530914410E-03,
1.384646189E-05, -9.625793620E-09, 2.519705809E-12, 7.108460860E+02,
-1.076003744E+01]
- [5.877124060E+05, -2.239249073E+03, 6.066949220E+00, -6.139685500E-04,
1.491806679E-07,  -1.923105485E-11, 1.061954386E-15, 1.283210415E+04,
-1.586640027E+01]
- [8.310139160E+08, -6.420733540E+05, 2.020264635E+02, -3.065092046E-02,
2.486903333E-06, -9.705954110E-11, 1.437538881E-15, 4.938707040E+06,
-1.672099740E+03]


### Shomate polynomials¶

The polynomial form described here, given for one or two temperature regions. Additional fields of a Shomate thermo entry are:

temperature-ranges

A list giving the temperature intervals on which the polynomials are valid. For one temperature region, this list contains the minimum and maximum temperatures for the polynomial. For two temperature regions, this list contains the minimum, intermediate, and maximum temperatures.

data

A list with one item per temperature region, where that item is a 7 item list of polynomial coefficients. The temperature regions are arranged in ascending order.

Example:

thermo:
model: Shomate
temperature-ranges: [298, 1300, 6000]
data:
- [25.56759, 6.096130, 4.054656, -2.671301, 0.131021,
-118.0089, 227.3665]
- [35.15070, 1.300095, -0.205921, 0.013550, -3.282780,
-127.8375, 231.7120]


### Constant heat capacity¶

The constant heat capacity model described here. Additional fields of a constant-cp thermo entry are:

T0

The reference temperature. Defaults to 298.15 K.

h0

The molar enthalpy at the reference temperature. Defaults to 0.0.

s0

The molar entropy at the reference temperature. Defaults to 0.0.

cp0

The heat capacity at constant pressure. Defaults to 0.0.

T-min

The minimum temperature at which this thermo data should be used. Defaults to 0.0.

T-max

The maximum temperature at which this thermo data should be used. Defaults to infinity.

Example:

thermo:
model: constant-cp
T0: 1000 K
h0: 9.22 kcal/mol
s0: -3.02 cal/mol/K
cp0: 5.95 cal/mol/K


### Piecewise Gibbs¶

A model based on piecewise interpolation of the Gibbs free energy as described here Additional fields of a piecewise-Gibbs entry are:

h0

The molar enthalpy at the reference temperature of 298.15 K. Defaults to 0.0.

dimensionless

A boolean flag indicating whether the values of the Gibbs free energy are given in a dimensionless form, that is, divided by $$RT$$. Defaults to false.

data

A mapping of temperatures to values of the Gibbs free energy. The Gibbs free energy can be either in molar units (if dimensionless is false) or nondimensionalized by the corresponding temperature (if dimensionless is true). A value must be provided at $$T^\circ = 298.15$$ K.

T-min

The minimum temperature at which this thermo data should be used. Defaults to 0.0.

T-max

The maximum temperature at which this thermo data should be used. Defaults to infinity.

Example:

thermo:
model: piecewise-Gibbs
h0: -230.015 kJ/mol
dimensionless: true
data: {298.15: -91.50963, 333.15: -85.0}


## Species equation of state models¶

model

String specifying the model to be used. Required. Supported model strings are:

## Species critical state parameters¶

critical-temperature

The critical temperature of the species.

critical-pressure

The critical pressure of the species.

acentric-factor

Pitzer’s acentric factor $$omega$$.

### Constant volume¶

A constant volume model as described here.

Any one of the following may be specified:

molar-volume

The molar volume of the species.

molar-density

The molar density of the species.

density

The mass density of the species.

Example:

equation-of-state:
model: constant-volume
molar-volume: 1.3 cm^3/mol


### Density temperature polynomial¶

A model in which the density varies with temperature as described here.

data

Vector of 4 coefficients for a cubic polynomial in temperature

Example:

equation-of-state:
model: density-temperature-polynomial
units: {mass: g, length: cm}
data: [0.536504, -1.04279e-4, 3.84825e-9, -5.2853e-12]


### HKFT¶

The Helgeson-Kirkham-Flowers-Tanger model as described here.

h0

Enthalpy of formation at the reference temperature and pressure

s0

Entropy of formation at the reference temperature and pressure

a

4-element vector containing the coefficients $$a_1, \ldots , a_4$$

c

2-element vector containing the coefficients $$c_1$$ and $$c_2$$

omega

The $$\omega$$ parameter at the reference temperature and pressure

Example:

equation-of-state:
model: HKFT
h0: -57433. cal/gmol
s0: 13.96 cal/gmol/K
a: [0.1839 cal/gmol/bar, -228.5 cal/gmol,
3.256 cal*K/gmol/bar, -27260. cal*K/gmol]
c: [18.18 cal/gmol/K, -29810. cal*K/gmol]
omega: 33060 cal/gmol


### Ideal gas¶

A species using the ideal gas equation of state, as described here. This model is the default if no equation-of-state section is included.

### Ions from neutral molecule¶

A species equation of state model used with the ions-from-neutral-molecule phase model, as described here.

special-species

Boolean indicating whether the species is the “special species” in the phase. Default is false.

multipliers

A dictionary mapping species to neutral species multiplier values.

Example:

equation-of-state:
model: ions-from-neutral-molecule
multipliers: {KCl(l): 1.2}


### Liquid Water IAPWS95¶

A detailed equation of state for liquid water as described here.

### Molar volume temperature polynomial¶

A model in which the molar volume varies with temperature as described here.

data

Vector of 4 coefficients for a cubic polynomial in temperature

### Redlich-Kwong¶

A model where species follow the Redlich-Kwong equation of state as described here.

a

Pure-species a coefficient. Scalar or list of two values for a temperature-dependent expression.

b

Pure-species b coefficient.

binary-a

Mapping where the keys are species and the values are the a coefficients for binary interactions between the two species.

## Species transport models¶

model

String specifying the model type. The only model that is specifically handled is gas.

### Gas transport¶

Species transport properties are a rare exception to Cantera’s use of SI units, and use the units in which these properties are customarily reported. No conversions are supported.

The additional fields of a gas transport entry are:

geometry

A string specifying the geometry of the molecule. One of atom, linear, or nonlinear.

diameter

The Lennard-Jones collision diameter [Å]

well-depth

The Lennard-Jones well depth [K]

dipole

The permanent dipole moment [Debye]. Default 0.0.

polarizability

The dipole polarizability [Å^3]. Default 0.0.

rotational-relaxation

The rotational relaxation collision number at 298 K [-]. Default 0.0.

acentric-factor

Pitzer’s acentric factor [-]. Default 0.0. This value may also be specified as part of the critical-parameters field, in which case the value provided there supersedes this one.

dispersion-coefficient

The dispersion coefficient, normalized by $$e^2$$ [Å^5]. Default 0.0.

quadrupole-polarizability

The quadrupole polarizability [Å^5]. Default 0.0.

Example:

transport:
model: gas
geometry: linear
well-depth: 107.4
diameter: 3.458
polarizability: 1.6
rotational-relaxation: 3.8