Atomic radius

The atomic_radius quantity exists to hold support datasets that are scientifically useful but should not be presented as direct condensed-phase vdW radii.

Rahm isodensity atomic radii (rahm2016)

This is currently the only built-in atomic-radius dataset.

• What it is: radii for isolated neutral atoms defined by the ρ = 0.001 e/bohr³ electron-density isosurface.
• Source idea: a consistent theory-based atomic size measure derived from computed electron densities.
• Coverage: broad, but not complete for the full periodic table.
• Why it matters here: it correlates well with structural vdW radii and is a useful support baseline when a condensed-phase target set is incomplete.
• How atomref uses it: support-only dataset for linear transfer into target vdW values such as alvarez2013.

This is an important example of the package philosophy: a dataset can be very useful algorithmically without being mislabeled as something it is not.