Model-chemistry zero-point energies

The zero-point energy implementation is checked against the quantum-chemistry outputs published with the model-chemistry benchmark by Green, Wu, Doner, and Pang. The source spans density-functional, double-hybrid, perturbation, and composite methods across many basis sets.

The validation script downloads qm_outputs.json from Zenodo record 14733712, verifies its checksum, and keeps the 55 MB source file outside the repository.

Run the benchmark

python scripts/validate_model_chemistry_zpe.py

No external electronic-structure engine is needed. ThermoScreening recomputes the zero-point energy directly from each source frequency spectrum.

Coverage

The script scans all 41,492 frequency records across 255 model chemistries. Eleven source rows have fewer modes than their geometries require; their exact identities are pinned and excluded. The remaining 41,481 records must be structurally valid.

A deterministic 1,000-record sample covers every one of the 255 model chemistries, evenly spaced records, and a seeded random remainder. The sample contains molecules with H, C, N, O, F, S, Cl, and Br and up to 26 atoms.

Results

Quantity	Mean absolute deviation	Maximum absolute deviation
Zero-point energy	0.345971 microhartree	1.459415 microhartree

The regression gate is 0.5 microhartree for the mean and 2.0 microhartree for the maximum. The residual is consistent with constants and rounding in the source outputs.

Interpretation

This benchmark validates frequency counting, unit conversion, and zero-point energy assembly over a much broader method and element matrix than QM9. It does not assess whether a particular electronic-structure method predicts an experimentally accurate frequency.

See the dataset publication for the model-chemistry definitions and scientific scope.