Accurate six-band nearest-neighbor tight-binding model for the pi-bands of bulk graphene and graphene nanoribbons

TL;DR

This paper introduces a new six-band tight-binding model for graphene's pi-bands that accurately captures asymmetries and edge effects, improving predictions of electronic properties in graphene nanoribbons.

Contribution

A novel three orbital per atom tight-binding model fitted to ab initio calculations that better reproduces graphene's pi-band asymmetries and edge passivation effects.

Findings

The model shows excellent agreement with DFT and GW calculations.

Significant differences in device performance predictions compared to simpler models.

Highlights the importance of accurate bandstructure modeling for graphene nanodevices.

Abstract

Accurate modeling of the pi-bands of armchair graphene nanoribbons (AGNRs) requires correctly reproducing asymmetries in the bulk graphene bands as well as providing a realistic model for hydrogen passivation of the edge atoms. The commonly used single-pz orbital approach fails on both these counts. To overcome these failures we introduce a nearest-neighbor, three orbital per atom p/d tight-binding model for graphene. The parameters of the model are fit to first-principles density-functional theory (DFT) - based calculations as well as to those based on the many-body Green's function and screened-exchange (GW) formalism, giving excellent agreement with the ab initio AGNR bands. We employ this model to calculate the current-voltage characteristics of an AGNR MOSFET and the conductance of rough-edge AGNRs, finding significant differences versus the single-pz model. These results show that an accurate bandstructure model is essential for predicting the performance of graphene-based nanodevices.