Widths of Autoionizing Resonances from TDDFT

Autoionizing resonances arising from a bound single excitation lying in the continuum can be captured with the usual adiabatic approximations for the exchange-correlation kernel of time-dependent density functional theory, but those arising from a double excitation cannot. We test a recently derived frequency-dependent kernel [Phys. Chem. Chem. Phys. 11, 4655 (2009)] for the width of the He atom 2s$^2$ resonance, and explore the sensitivity on the ground-state approximation used.