Outer-valence Green's function method using natural orbitals for ultrafast electron density dynamics

We use the outer-valence Green's function (OVGF) method as one-particle theory for the description of ultrafast electron charge density dynamics after ionization of an outer-valence electron. When strong hole mixing of the states involved occurs, the OVGF provides a poor description of this effect; this shortcoming is however remedied, when the OVGF is combined with a natural orbital basis obtained by post-Hartree-Fock methods. We demonstrate our approach on the 3-methylen-4-penten-N,N-dimethylamine molecule, which exhibits oscillatory charge motion from the chromophore-donor to the amine-acceptor site with a period of about 7 fs after ionization of an electron from its highest occupied molecular orbital. Our results are in very good agreement with results obtained using the third-order algebraic diagrammatic construction scheme.