Electronegativity
Reparametrization — r = 0.94–0.96 — the γ proxy is ionization energy renamedElectronegativity — how strongly an atom attracts electrons in a bond — correlates with the archive's optical γ proxy at r = 0.94–0.96. That proxy is defined as γoptical = 13.6 eV / IE, where IE is the ionization energy, so the correlation is electronegativity against ionization energy: a textbook relation that Mulliken's definition of electronegativity, χ = (IE + EA)/2, builds in. (Until 2026-11-02 this page gave r = 0.979. That number is chemical softness against the same 1/IE, archive session #118; site explorer audit 2026-10-31.)
Why This Works
Electronegativity measures the strength of electron-atom coupling. High electronegativity (fluorine: 3.98) means electrons are tightly bound, highly correlated with the nucleus. Low electronegativity (cesium: 0.79) means electrons are loosely held, weakly correlated.
This is a direct expression of Ncorr: how many particles (electrons + nucleus) are moving as a correlated unit determines both the electronegativity and the γ value.
Circularity via bonding character (explorer finding, 2026-05-06)
The site's documented Ncorr methods include an entropy-ratio method whose inputs (Suncorrelated, Seffective) depend on bonding character — covalent vs. ionic vs. metallic — through vibrational density of states and cohesive energy. Electronegativity is the operational measure of bonding ionicity (bond ionicity ∝ (χA − χB)²), so under that method electronegativity enters γ through the same bonding-character variable it is then correlated against. No method that avoids this overlap has been shown applied to this dataset. See Chemistry Correlation Explorer for the same caveat applied to the wider cohort.
The number did not come from that route (site explorer audit, 2026-10-31). The script that produced the electronegativity correlation does not use an entropy-ratio Ncorr. It sets γoptical = 13.6 eV / IE, so the circularity is more direct than the one described above: the proxy is the inverse ionization energy. The “Why This Works” story above (electrons and nucleus moving as a correlated unit) is an interpretation laid over that relation, not something the calculation tested.
Connection to Sound Velocity
Both sound velocity (r = 0.982) and electronegativity (r = 0.94–0.96) correlate with γ for the same reason: they both measure aspects of collective coupling. Sound velocity measures atom-atom coupling; electronegativity measures electron-atom coupling. The coherence function captures the underlying correlation structure that drives both. Both correlations carry the circularity caveat above — see Sound Velocity for that page's additional sign-inversion problem, which is specific to density-defined quantities and has not been separately checked for electronegativity.