pub const COULOMB_E2: f64 = _; // 2.307077550778355E-28f64Expand description
Coulomb constant e² / (4π ε₀), J m. Derived from ELEMENTARY_CHARGE
(C) and VACUUM_PERMITTIVITY (F/m = C²/(J m)), so the unit is J m
(about 2.307e-28 J m, i.e. 14.3996 eV Å). CODATA lists no row for this
combination; its relative uncertainty is that of ε₀, 1.6e-10. This is the
combination the screened-Coulomb interatomic potentials in the ion engine
are written with.