Investigation of ionization energies and photoelectron cross-section of semiconductor quantum dots beyond the electric dipole approximation

This work presents a computation investigation of the photoionization process in a series of PbS and CdS quantum dots without making the dipole approximation in the light-matter interaction Hamiltonian. Photoionization of quantum dots provides important information about the occupied energy levels and can provide insight into their electronic and photochemical properties. Typically light-matter interaction in quantum dots is treated using electric-dipole approximation. However, going beyond the dipole approximation becomes critical for understanding interactions with high-energy photons. In this work, we have combined the 2nd-order electron-propagator method with the stochastic enumeration technique to construct a stochastic self-energy operator. The ionization energies were obtained from the self-consistent solution of the resulting Dyson equation.  The photoionization cross-section was calculated in a mixed Gaussian-plane wave basis and was calculated using the fully complex response kernel. The calculation was performed for a series of PbS and CdS quantum dots and the results for the ionization energies, pole-strengths, and the photoelectron spectra in the X-ray and XUV region for these systems will be presented. Comparisons between the complex-response kernel and the dipole-approximation results will be discussed. The results from this study show the importance of non-dipolar effects for understanding light-matter interaction in semiconductor quantum dots.