Correct the G4 harmonic frequency scale factor to 0.9992 - #1039
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The G4 entry added in #1004 carries 0.994, derived as 0.980 * 1.014 where 0.980 was refitted with Truhlar's method over the 15-species standard set. G4 is a composite method that defines its own ZPE scale factor: 0.9854, applied to the B3LYP/6-31G(2df,p) frequencies the method prescribes (Curtiss, Redfern and Raghavachari 2007). Refitting it produces a number that disagrees with the method's own definition. Use the method's factor in the field's units: 0.9854 * 1.014 = 0.9992. This also restores consistency with the neighbouring composite entry. cbs-qb3 stores its own method-defined ZPE factor the same way (0.99 * 1.014), so a refit for G4 alone made the two entries mean different things. Adds source 6 for the G4 paper; no existing source id covered it. Effect: relative to no entry at all, the ZPE shift is 0.02-0.10 kcal/mol. Relative to the 0.994 this replaces, values computed with the old entry are low by 0.0059 * ZPE_harm -- 0.15 kcal/mol for a small species, 0.6+ kcal/mol at ZPE ~ 120 kcal/mol. That correction is closed-form per species, so data already computed against 0.994 is recoverable without a re-run.
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The change is a straightforward, internally consistent data correction with valid YAML structure and updated provenance.
Pull request overview
This PR updates ARC’s frequency scale-factor reference data to reflect G4’s method-defined ZPE scaling constant, improving consistency with how other composite methods (e.g., CBS-QB3) are represented in the table.
Changes:
- Updates the
g4, software: gaussianfactor from0.994to0.9992(i.e.,0.9854 * 1.014). - Replaces the G4 entry’s provenance to cite the G4 paper and adds it as
source: 6. - Updates the note to reflect the method-defined ZPE scale factor basis.
File summaries
| File | Description |
|---|---|
data/freq_scale_factors.yml |
Corrects the G4 scale factor value and cites the primary G4 reference in the sources table. |
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What
Changes the
g4, software: gaussianentry indata/freq_scale_factors.ymlfrom 0.994 to 0.9992, re-points its provenance to the G4 paper, and adds source6for that reference.Why
The G4 entry added in #1004 was derived as
0.980 * 1.014, where0.980came from refitting the ZPE scale factor with Truhlar's method over the 15-species standard set.G4 is a composite method that defines its own ZPE scale factor —
0.9854, applied to the B3LYP/6-31G(2df,p) frequencies the method prescribes (Curtiss, Redfern & Raghavachari, J. Chem. Phys. 126, 084108, 2007). Refitting that constant produces a number in disagreement with the method's own definition, which is not what the table is for.In the field's units the entry should therefore be
0.9854 * 1.014 = 0.9992.This also restores consistency with the neighbouring composite entry:
cbs-qb3stores its own method-defined ZPE factor the same way (0.99 * 1.014). Refitting for G4 alone left the two composite entries meaning different things.Effect
0.0059 * ZPE_harm— about 0.15 kcal/mol for a small species and 0.6+ kcal/mol at ZPE ≈ 120 kcal/mol.That correction is closed-form per species and needs only the harmonic ZPE, which is in the logs — so anything already computed against
0.994is recoverable without a re-run.Checks
data/freq_scale_factors.ymlparses; the key resolves to0.9992withsource: 6.0.994occurrences inarc/utils/scale_test.pybelong tocbs-qb3andb2plypd3/def2tzvpin a synthetic scale-driver test and are untouched.