Theory of Linear Optical Absorption in Diamond Shaped Graphene Quantum Dots

TL;DR

This study investigates the optical and electronic properties of diamond-shaped graphene quantum dots using large-scale electron-correlated calculations, revealing size-dependent spectral shifts and emphasizing the importance of electron correlations over tight-binding predictions.

Contribution

It introduces a detailed electron-correlation computational approach to accurately predict optical spectra of graphene quantum dots, contrasting with simpler models.

Findings

Absorption spectra are red-shifted with increasing quantum dot size.

The first optical absorption peak is not the most intense, aligning with experimental data.

Electron-correlation effects significantly influence optical properties, unlike tight-binding models.

Abstract

In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) have been studied by employing large-scale electron-correlated calculations. The computations have been performed using the \pi-electron Pariser-Parr-Pople model Hamiltonian, which incorporates long-range Coulomb interactions. The influence of electron-correlation effects on the ground and excited states has been included by means of the configuration-interaction approach, used at various levels. Our calculations have revealed that the absorption spectra are red-shifted with the increasing sizes of quantum dots. It has been observed that the first peak of the linear optical absorption, which represents the optical gap, is not the most intense peak. This result is in excellent agreement with the experimental data, but in stark contrast to the predictions of the tight-binding model, according to which the first peak is the most intense peak, pointing to the importance of electron-correlation effects.