Excited States and Optical Properties of Hydrogen-Passivated Rectangular Graphenes: A Computational Study

TL;DR

This computational study investigates the excited states and optical properties of hydrogen-passivated rectangular graphene-like molecules using electron-correlated methods, revealing size-dependent electronic characteristics and agreement with experimental spectra.

Contribution

It introduces a large-scale, electron-correlated computational approach to accurately predict optical and spin gaps in rectangular graphene-like molecules, emphasizing the role of electron correlation.

Findings

Optical spectra agree well with experiments.

Ground states develop diradical character with size.

Spin gaps decrease as molecule size increases.

Abstract

In this paper, we perform large-scale electron-correlated calculations of optoelectronic properties of rectangular graphene-like polycyclic aromatic hydrocarbon molecules. Theoretical methodology employed in this work is based upon Pariser-Parr-Pople (PPP) $\pi$-electron model Hamiltonian, which includes long-range electron-electron interactions. Electron-correlation effects were incorporated using multi-reference singles-doubles configuration-interaction (MRSDCI) method, and the ground and excited state wave functions thus obtained were employed to calculate the linear optical absorption spectra of these molecules, within the electric-dipole approximation. As far as the ground state wave functions of these molecules are concerned, we find that with the increasing size, they develop a strong diradical open-shell character. Our results on optical absorption spectra are in very good agreement with the available experimental results, outlining the importance of electron-correlation effects in accurate description of the excited states. In addition to the optical gap, spin gap of each molecule was also computed using the same methodology. Calculated spin gaps exhibit a decreasing trend with the increasing sizes of the molecules, suggesting that the infinite graphene has a vanishing spin gap.