The objective of this work is to characterize the effect of quantum confinement on the ionization potential of a series of PbS quantum dots. The ionization potential of quantum dots provide important information about the valence band states and can provide insight into electron-transfer and electron-detachment processes. Experimentally, they can be obtained from x-ray and UV photoemission spectroscopy.<br/>In this work, we present a first-principles computational investigation of the effect of increasing dot size of PbS nanoparticles on the ionization potential. This was achieved by combining Green's function theory with the recently developed stochastically-enumerated stratified sampling of molecular orbitals (SESSMO) method for solving the Dyson equation. The calculated ionization potentials were found to decrease with increasing dot size, although the trend was not found to be monotonic. The non-monotonic behavior was attributed to the strong dependence of the IPs on the structure of the quantum dots. Electron-electron correlation was found to be essential, and IPs calculated from the Dyson equation were found to be different from Koopman's approximation IPs. This highlights the need for a high-level method for understanding and predicting size-dependent trends in QDs. The results show that the IPs of the quantum dots can be significantly impacted by distortion in geometry and coupling to vibrational degrees of freedom.

Investigation of size-dependent ionization potentials of PbS quantum dots

ACS Spring 2022

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