Accurate Rydberg excitations from the local density approximation.

Despite the incorrect asymptotic behavior of its potential, the time-dependent local density approximation can yield accurate optical spectra. The oscillator strengths of Rydberg excitations appear in the calculated spectrum as continuum contributions with excellent optical intensity. We explain why, illustrate this for the neon and helium atoms, and also discuss when such calculations of the optical response will be inaccurate.