# rmgpy.thermo.NASAPolynomial¶

class rmgpy.thermo.NASAPolynomial(coeffs=None, Tmin=None, Tmax=None, E0=None, comment='')

A heat capacity model based on the NASA polynomial. Both the seven-coefficient and nine-coefficient variations are supported. The attributes are:

Attribute Description
coeffs The seven or nine NASA polynomial coefficients
Tmin The minimum temperature in K at which the model is valid, or zero if unknown or undefined
Tmax The maximum temperature in K at which the model is valid, or zero if unknown or undefined
E0 The energy at zero Kelvin (including zero point energy)
comment Information about the model (e.g. its source)

The NASA polynomial is another representation of the heat capacity, enthalpy, and entropy using seven or nine coefficients $$\mathbf{a} = \left[a_{-2}\ a_{-1}\ a_0\ a_1\ a_2\ a_3\ a_4\ a_5\ a_6 \right]$$. The relevant thermodynamic parameters are evaluated via the expressions

$\frac{C_\mathrm{p}(T)}{R} = a_{-2} T^{-2} + a_{-1} T^{-1} + a_0 + a_1 T + a_2 T^2 + a_3 T^3 + a_4 T^4$
$\frac{H(T)}{RT} = - a_{-2} T^{-2} + a_{-1} T^{-1} \ln T + a_0 + \frac{1}{2} a_1 T + \frac{1}{3} a_2 T^2 + \frac{1}{4} a_3 T^3 + \frac{1}{5} a_4 T^4 + \frac{a_5}{T}$
$\frac{S(T)}{R} = -\frac{1}{2} a_{-2} T^{-2} - a_{-1} T^{-1} + a_0 \ln T + a_1 T + \frac{1}{2} a_2 T^2 + \frac{1}{3} a_3 T^3 + \frac{1}{4} a_4 T^4 + a_6$

In the seven-coefficient version, $$a_{-2} = a_{-1} = 0$$.

As simple polynomial expressions, the NASA polynomial is faster to evaluate when compared to the Wilhoit model; however, it does not have the nice physical behavior of the Wilhoit representation. Often multiple NASA polynomials are used to accurately represent the thermodynamics of a system over a wide temperature range; the NASA class is available for this purpose.

Cp0

The heat capacity at zero temperature.

CpInf

The heat capacity at infinite temperature.

E0

The ground state energy (J/mol) at zero Kelvin, including zero point energy, or None if not yet specified.

Tmax

The maximum temperature at which the model is valid, or None if not defined.

Tmin

The minimum temperature at which the model is valid, or None if not defined.

c0

c0: ‘double’

c1

c1: ‘double’

c2

c2: ‘double’

c3

c3: ‘double’

c4

c4: ‘double’

c5

c5: ‘double’

c6

c6: ‘double’

changeBaseEnthalpy(self, double deltaH)

Add deltaH in J/mol to the base enthalpy of formation H298.

cm1

cm1: ‘double’

cm2

cm2: ‘double’

coeffs

The set of seven or nine NASA polynomial coefficients.

comment

comment: str

discrepancy(self, HeatCapacityModel other) → double

Return some measure of how dissimilar self is from other.

The measure is arbitrary, but hopefully useful for sorting purposes. Discrepancy of 0 means they are identical

getEnthalpy(self, double T) → double

Return the enthalpy in J/mol at the specified temperature T in K.

getEntropy(self, double T) → double

Return the entropy in J/mol*K at the specified temperature T in K.

getFreeEnergy(self, double T) → double

Return the Gibbs free energy in J/mol at the specified temperature T in K.

getHeatCapacity(self, double T) → double

Return the constant-pressure heat capacity in J/mol*K at the specified temperature T in K.

isIdenticalTo(self, HeatCapacityModel other) → bool

Returns True if self and other report very similar thermo values for heat capacity, enthalpy, entropy, and free energy over a wide range of temperatures, or False otherwise.

isSimilarTo(self, HeatCapacityModel other) → bool

Returns True if self and other report similar thermo values for heat capacity, enthalpy, entropy, and free energy over a wide range of temperatures, or False otherwise.

isTemperatureValid(self, double T) → bool

Return True if the temperature T in K is within the valid temperature range of the thermodynamic data, or False if not. If the minimum and maximum temperature are not defined, True is returned.