Data Sources¶

Thermodynamic data sources used by PHOENIX.

Primary Sources¶

pgradd (Benson Group Additivity)¶

Library: pgradd

Purpose: Primary source for thermodynamic estimation

Properties: - Enthalpy of formation (ΔHf°) - Entropy (S°) - Heat capacity (Cp)

Data Coverage: - Organic compounds with common functional groups - Temperature range: 298-1500 K (best accuracy)

Method: Benson Group Additivity with NASA polynomial coefficients

Usage in PHOENIX:

from pgradd import ThermoChem
# PHOENIX wraps pgradd for Benson GA estimation

chemicals (CalebBell/ChEDL)¶

Library: chemicals

Purpose: Reference thermodynamic data

Data Sources Included: - NIST WebBook - Yaws' Handbook - DIPPR database - CRC Handbook - Various literature sources

Properties: - Formation enthalpies - Standard entropies - Heat capacities - Vapor pressures - Critical properties

Usage in PHOENIX:

from chemicals import Hf, S0
# Used for reference value comparison

NIST-JANAF Tables¶

Source: NIST Standard Reference Database 69

Purpose: High-accuracy reference data for common compounds

Coverage: - ~2000 substances - High-temperature data (0-6000 K for many) - Experimental values with uncertainties

Properties: - ΔHf°, S°, Cp, H°, G° - Phase transition data

Accuracy: Generally ±1-5 kJ/mol for ΔHf°

Decomposition Products¶

Formation Enthalpies¶

Values used for decomposition calculations:

Product	ΔHf° (kJ/mol)	Source
HF	-273.30	NIST
N₂	0.00	Reference
P₄O₁₀	-2984.0	CRC
H₂O (g)	-241.83	NIST
CO₂	-393.52	NIST
SO₂	-296.81	NIST
CO	-110.53	NIST
HCl	-92.31	NIST
HBr	-36.29	NIST
C (graphite)	0.00	Reference
H₂	0.00	Reference
S (rhombic)	0.00	Reference
Br₂ (g)	30.91	NIST

Data Hierarchy¶

PHOENIX uses data in this priority order:

For Thermodynamic Estimation¶

pgradd (Benson GA) - Primary estimation
chemicals - Fallback if Benson GA fails
Hardcoded values - For decomposition products

For Reference Comparison¶

NIST WebBook (via chemicals)
Yaws' Handbook (via chemicals)
Literature values

Accuracy Assessment¶

Benson GA (pgradd)¶

Compound Type	Typical Error (ΔHf°)
Alkanes	±2-5 kJ/mol
Alcohols, ethers	±5-8 kJ/mol
Ketones, aldehydes	±5-10 kJ/mol
Aromatic	±5-10 kJ/mol
Nitro compounds	±10-20 kJ/mol
Strained rings	±10-30 kJ/mol

Reference Data (chemicals)¶

Source	Typical Uncertainty
NIST experimental	±1-5 kJ/mol
Yaws compilation	±5-15 kJ/mol
Estimated values	±10-30 kJ/mol

Data Limitations¶

Benson GA Limitations¶

Missing Groups
Unusual bonding patterns
Rare functional groups
Some organometallic fragments
Accuracy Degradation
Strained ring systems
Multiple adjacent functional groups
Very large molecules (>100 atoms)
Phase Corrections
Primarily gas-phase data
Liquid/solid corrections less reliable

Reference Data Limitations¶

Coverage Gaps
Many compounds lack experimental data
High-temperature data sparse
Consistency Issues
Different sources may disagree
Temperature/phase not always specified

Validation¶

Built-in Validation¶

PHOENIX can compare estimates to reference values:

hf = compound.enthalpy_of_formation

if hf.has_reference():
    print(f"Estimated: {hf.value:.1f} kJ/mol")
    print(f"Reference: {hf.reference_value.value:.1f} kJ/mol")
    print(f"Deviation: {hf.deviation:.1f} kJ/mol")

Recommended Validation¶

For safety-critical applications:

Compare Benson GA to experimental data
Check multiple reference sources
Validate with experimental measurements

Adding Custom Data¶

PHOENIX does not currently support custom data injection.

For custom data needs: 1. Use RDKit for molecular processing 2. Implement custom estimation methods 3. Query external databases directly

References¶

pgradd¶

@software{pgradd,
  author = {NREL},
  title = {pgradd: Python Group Additivity},
  url = {https://github.com/NREL/pgradd}
}

chemicals¶

@software{chemicals,
  author = {Bell, Caleb},
  title = {chemicals: Chemical properties component of ChEDL},
  url = {https://github.com/CalebBell/chemicals}
}

NIST¶

@misc{nist_webbook,
  author = {NIST},
  title = {NIST Chemistry WebBook},
  url = {https://webbook.nist.gov/chemistry/}
}