Fourth order many-body Green’s function: Application of a simplified model to the ionization energies of N2

Publisher Website
Google Scholar
Abstract
In the framework of the recently proposed ADC (algebraic diagrammatic construction) approximation scheme to the one particle Green’s function (1p‐GF), a study of the fourth order approximation on the valence shell ionization spectrum of N2 with two different basis sets is presented. The effects of the various fourth order terms on the structure of the 1p‐GF are discussed. It is shown that some conclusions of this work agree with the limited experience existing on the subject, while some others are new. The effect on the structure of the satellite lines of some fourth order contributions, which have been ignored in the literature so far, are shown to be relevant in order to achieve even qualitatively a good description of the inner valence shell ionization processes, especially in the case of a breakdown of the molecular orbital picture of the ionization. As a result of this investigation a computational model of the fourth order approximation to the 1p‐GF is proposed. It is expected to be more reliable than the existing ones. This model should be computationally tractable at least for di‐ and triatomic first‐row molecules. Finally, the complete valence shell spectrum of N2 within an extended basis set is calculated and a comparison is made with the experiment as well as with other theoretical results.