Graphene quantum dots in various many-electron π-models

Abstract

We make use of various quantum chemistry approaches to understand π-electronic properties of a number of graphene quantum dots (GQDs) and at the same time to clarify the possibilities of fairly simple and feasible models for complex carbon-containing systems. Most of the studied systems turn out to be electronically unstable and requiring a good account for electron correlation. Here we investigate the ground state properties of GQDs in the framework of Löwdin’s extended Hartree-Fock method for π-shells. Additionally, GQD-excited states are modeled by the restricted active space configuration interaction (RAS-CI) method. In particular, it is shown that RAS-CI allows to get reasonable singlet-triplet energy gaps whereas the conventional single CI method gives mostly incorrect results for the same systems. Special focuses are given to aromaticity, effective electron unpairing, and the behavior of graphene networks in strong electric fields.