A comparative study of density functional and density functional tight binding calculations of defects in graphene

TL;DR

This study compares the accuracy of DFTB and DFT methods in modeling defects in graphene, demonstrating DFTB's effectiveness for structures, energies, and defect dynamics, including irradiation damage simulations.

Contribution

It provides a comprehensive comparison between DFTB and DFT for defect calculations in graphene, highlighting DFTB's reliability and potential for dynamic defect simulations.

Findings

DFTB accurately reproduces defect structures and energies.

Migration barriers are well-matched between DFTB and DFT.

DFTB shows promise for simulating defect dynamics like irradiation damage.

Abstract

The density functional tight binding approach (DFTB) is well adapted for the study of point and line defects in graphene based systems. After briefly reviewing the use of DFTB in this area, we present a comparative study of defect structures, energies and dynamics between DFTB results obtained using the dftb+ code, and density functional results using the localised Gaussian orbital code, AIMPRO. DFTB accurately reproduces structures and energies for a range of point defect structures such as vacancies and Stone-Wales defects in graphene, as well as various unfunctionalised and hydroxylated graphene sheet edges. Migration barriers for the vacancy and Stone-Wales defect formation barriers are accurately reproduced using a nudged elastic band approach. Finally we explore the potential for dynamic defect simulations using DFTB, taking as an example electron irradiation damage in graphene.