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Implements NASA polynomial fit with pinned reference value #726

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Merged
avcopan merged 1 commit into from
May 21, 2026
Merged

Implements NASA polynomial fit with pinned reference value #726

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4 changes: 2 additions & 2 deletions src/autochem/therm/_species.py
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Original file line number Diff line number Diff line change
Expand Up @@ -195,8 +195,8 @@ def pac99_input_string(
Hf298 = spc.therm.enthalpy_of_formation(units={"energy": "J"}) # noqa: N806
Ts = spc.therm.T # noqa: N806
# Enthalpy units are set to kJ by "KJOULE" keyword below
dH298 = spc.therm.delta_enthalpy(T=298, method="nearest", units={"energy": "kJ"}) # noqa: N806
dHs = spc.therm.delta_enthalpy_data(units={"energy": "kJ"}) # noqa: N806
dH298 = spc.therm.thermal_enthalpy(T=298, method="nearest", units={"energy": "kJ"}) # noqa: N806
dHs = spc.therm.thermal_enthalpy_data(units={"energy": "kJ"}) # noqa: N806
# Entropy and heat capacity are always in Joules
# (see https://ntrs.nasa.gov/citations/19930003779, p. 33)
Ss = spc.therm.entropy_data(P=1, units={"pressure": "bar", "energy": "J"}) # noqa: N806
Expand Down
75 changes: 37 additions & 38 deletions src/autochem/therm/data.py
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Original file line number Diff line number Diff line change
Expand Up @@ -72,7 +72,7 @@ def plot_data(
Key.Cp: heat_capacity_constant_pressure,
Key.S: entropy,
Key.H: enthalpy,
Key.dH: delta_enthalpy,
Key.dH: thermal_enthalpy,
}

x_data = np.linspace(*T_range, num=1000)
Expand Down Expand Up @@ -181,7 +181,7 @@ def plot_data(
Key.Cp: heat_capacity_constant_pressure,
Key.S: entropy,
Key.H: enthalpy,
Key.dH: delta_enthalpy,
Key.dH: thermal_enthalpy,
}

(i_,) = np.where(
Expand Down Expand Up @@ -241,10 +241,10 @@ def __init__(

if int(Tf) == 0:
# Access through __dict__ here since model is frozen
self.__dict__["Hf"] += self.delta_enthalpy(
self.__dict__["Hf"] += self.thermal_enthalpy(
T=298,
method="nearest",
) - elemental_delta_enthalpy_room_temperature(self.formula)
) - elemental_thermal_enthalpy_room_temperature(self.formula)
elif int(Tf) != 298:
msg = f"Invalid reference temperature Tf = {Tf}"
raise ValueError(msg)
Expand All @@ -268,7 +268,7 @@ def data_set(self) -> xarray.Dataset:
Key.Cv: self.heat_capacity_data(const="V"),
Key.Cp: self.heat_capacity_data(const="P"),
Key.S: self.entropy_data(),
Key.dH: self.delta_enthalpy_data(),
Key.dH: self.thermal_enthalpy_data(),
}
return xarray.Dataset(
data_vars={k: ([coord_key], v) for k, v in data_arrs.items()},
Expand Down Expand Up @@ -373,14 +373,14 @@ def enthalpy_data(self, units: UnitsData | None = None) -> NDArray[np.float64]:
:param units: Units
:return: Enthalpy
"""
return self.Hf + self.delta_enthalpy_data() - self.delta_enthalpy(T=298.15)
return self.Hf + self.thermal_enthalpy_data() - self.thermal_enthalpy(T=298.15)

@unit_.manage_units([], D.energy_per_substance)
def delta_enthalpy_data(
def thermal_enthalpy_data(
self,
units: UnitsData | None = None, # noqa: ARG002
) -> NDArray[np.float64]:
"""Calculate delta enthalpy data.
"""Calculate thermal enthalpy data.

Formula:

Expand Down Expand Up @@ -450,12 +450,12 @@ def enthalpy(
"""
return (
self.Hf
+ self.delta_enthalpy(T=T, method=method)
- self.delta_enthalpy(T=298.15, method=method)
+ self.thermal_enthalpy(T=T, method=method)
- self.thermal_enthalpy(T=298.15, method=method)
)

@unit_.manage_units([], D.energy_per_substance)
def delta_enthalpy(
def thermal_enthalpy(
self,
T: ArrayLike, # noqa: N803
units: UnitsData | None = None, # noqa: ARG002
Expand Down Expand Up @@ -582,19 +582,19 @@ def enthalpy(
funcs = [calc.enthalpy for calc in self.piecewise_calculators()]
return np.piecewise(T, conds, funcs)

def delta_enthalpy(
def thermal_enthalpy(
self,
T: ArrayLike, # noqa: N803
units: UnitsData | None = None, # noqa: ARG002
) -> NDArray[np.float64]:
"""Evaluate enthalpy change, dH(T).
"""Evaluate thermal enthalpy, H(T) - H(0).

:param T: Temperature(s)
:param units: Unit system
:return: Function value(s)
"""
conds = self.piecewise_conditions(T)
funcs = [calc.delta_enthalpy for calc in self.piecewise_calculators()]
funcs = [calc.thermal_enthalpy for calc in self.piecewise_calculators()]
return np.piecewise(T, conds, funcs)

@classmethod
Expand Down Expand Up @@ -642,26 +642,26 @@ def fit( # noqa: PLR0913
) -> "Nasa7ThermFit":
"""Fit data to Nasa-7 therm fit object.

Construct a matrix mapping (unknown) polynomial coefficients to property values.
Parametrization:

Cp/R = a1 + a2 T + a3 T^2 + a4 T^3 + a5 T^4
S/R = a1 ln(T) + a2 T + (a3/2) T^2 + (a4/3) T^3 + (a5/4) T^4 + a7
H/R = a1 T + (a2/2) T^2 + (a3/3) T^3 + (a4/4) T^4 + (a5/5) T^5 + a6
Cp/R = A0 + A1 T + A2 T^2 + A3 T^3 + A4 T^4
H/R = A0 T + (A1/2) T^2 + (A2/3) T^3 + (A3/4) T^4 + (A4/5) T^5 + A5
S/R = A0 ln(T) + A1 T + (A2/2) T^2 + (A3/3) T^3 + (A4/4) T^4 + A6

1. Reduced linear equation for A0 - A4:

The matrix is solved using least squares to find the polynomial coefficients:
[t1 - 1, t1^2 - 1, t1^3 - 1, t1^4 - 1] [a1] [(Cp(T1) - Cp(T_ref))/R]
[t2 - 1, t2^2 - 1, t2^3 - 1, t2^4 - 1] [a2] = [(Cp(T2) - Cp(T_ref))/R]
[ ..., ..., ..., ...] [a3] [ ...]
[tN - 1, tN^2 - 1, tN^3 - 1, tN^4 - 1] [a4] [(Cp(TN) - Cp(T_ref))/R]

[ 1, T1, T1^2, T1^3, T1^4, 0, 0] [Cp(T1)/R]
[ 1, T2, T2^2, T2^3, T2^4, 0, 0] [a1] [Cp(T2)/R]
[ ..., ..., ..., ..., ..., 0, 0] [a2] [ ... ]
[ln(T1), T1, (1/2)T1^2, (1/3)T1^3, (1/4)T1^4, 0, 1] [a3] [ S(T1)/R]
[ln(T2), T2, (1/2)T2^2, (1/3)T2^3, (1/4)T2^4, 0, 1] [a4] = [ S(T2)/R]
[ ..., ..., ..., ..., ..., 0, 1] [a5] [ ... ]
[ T1, T1^2, (1/3)T1^3, (1/4)T1^4, (1/5)T1^5, 1, 0] [a6] [ H(T1)/R]
[ T2, T2^2, (1/3)T2^3, (1/4)T2^4, (1/5)T2^5, 1, 0] [a7] [ H(T2)/R]
[ ..., ..., ..., ..., ..., 1, 0] [ ... ]
t = T / T_ref

Dimension: 3*n_T x 7 (n_T = number of temperature values)
A0 = Cp(T_ref) / R - (a1 + a2 + a3 + a4)
A1 = a1 / T_ref
A2 = a2 / T_ref^2
A3 = a3 / T_ref^3
A4 = a4 / T_ref^4

:param T: Temperatures
:param Cp: Constant-pressure heat capacities
Expand All @@ -678,10 +678,9 @@ def fit( # noqa: PLR0913
H = np.array(H, dtype=np.float64) # noqa: N806
T_min = T_min or np.min(T) # noqa: N806
T_max = T_max or np.max(T) # noqa: N806
low = (T_min <= T) & (T_mid >= T)
high = (T_mid <= T) & (T_max >= T)
calc_low = Nasa7Calculator.fit(T=T[low], Cp=Cp[low], S=S[low], H=H[low])
calc_high = Nasa7Calculator.fit(T=T[high], Cp=Cp[high], S=S[high], H=H[high])
calc_low, calc_high = Nasa7Calculator.fit(
T=T, Cp=Cp, S=S, H=H, T_min=T_min, T_mid=T_mid, T_max=T_max
)
return cls(
formula=formula,
charge=charge,
Expand Down Expand Up @@ -776,18 +775,18 @@ def enthalpy(
return therm.enthalpy(T=T, units=units)


def delta_enthalpy(
def thermal_enthalpy(
therm: ThermCalculator,
T: ArrayLike, # noqa: N803
units: UnitsData | None = None,
) -> NDArray[np.float64]:
"""Evaluate enthalpy change, dH(T).
"""Evaluate thermal enthalpy, H(T) - H(0).

:param T: Temperature(s)
:param units: Unit system
:return: Function value(s)
"""
return therm.delta_enthalpy(T=T, units=units)
return therm.thermal_enthalpy(T=T, units=units)


# Conversions
Expand Down Expand Up @@ -1059,10 +1058,10 @@ def display( # noqa: PLR0913
}


def elemental_delta_enthalpy_room_temperature(
def elemental_thermal_enthalpy_room_temperature(
formula: FormulaData,
) -> float:
"""Get change in enthalpy of formation 0 K to room temperature (298 K).
"""Get change in thermal enthalpy of formation 0 K to room temperature (298 K).

:param formula: Formula
"""
Expand Down
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