Green's-Function Approach for 3- and 4-Particle Correlated Excitations: Trions and Biexcitons*

The ab initio GW plus Bethe-Salpeter equation (GW-BSE) approach is a quantitatively accurate formalism to describe neutral excitations in systems of various electronic structure and dimensionality. However, higher-order excitations involving more than two quasiparticles are not readily obtained from this formalism. These excitations include trions and biexcitons. The latter can be exploited, for instance, to design solar-cell devices that go beyond the Shockley-Queisser limit. In this work, we describe a new approach based on the interacting Green’s function formalism to compute these excitations from first principles. We describe how we cast the problem of finding trion and biexciton excitations rigorously into a Dyson-like equation. We also present first-principles calculations of trions and biexcitons on single-wall carbon nanotubes.