Effect of Point Defects on Optical Properties of Graphene Fluoride: A First-Principles Study

Abstract

The experimental optical gap of graphene fluoride has been measured between 3.1 and 3.8 eV, which is much smaller than the corresponding theoretical predictions (∼5.1–5.7 eV). To resolve this discrepancy, we examine the optical properties of graphene fluoride in the presence of point defects. We employ a first-principles method for large-scale calculations of electronic excitations in solids based on density functional theory with optimally tuned and range-separated hybrid (OT-RSH) functionals. The method is validated for lithium fluoride, graphene fluoride, and phosphorene with excellent agreement to previous computational and experimental results. We reveal that the optoelectronic properties of graphene fluoride can be influenced profoundly by a small amount of fluorine vacancies and exciton binding energy in graphene fluoride can be doubled by a small concentration of oxygen substitutional defects. These point defects are believed to be responsible for the discrepancy in the optical gaps between the theory and experiments.

Density functionals with asymptotic-potential corrections are required for the simulation of spectroscopic properties of materials

“…Density functionals with asymptotic correction, designed for materials only applications, are now also becoming widely available, [33][34][35] and offer solutions for silicon and related problems, whilst more generally applicable asymptotically correct methods are currently also being devised. 23,[36][37][38][39][40][41][42][43][44] Optimal methods that are independent of dimensionality will provide the opportunity for unified understanding of molecular and materials spectroscopies.…”

“…Please do not adjust margins recent efforts, 23,[36][37][38][39][40][41][42][43][44] reflecting many and varied design choices. Whilst we consider mostly CAM-B3LYP herein, the elucidated basic principles are expected to be qualitatively representative of all asymptotically corrected functionals.…”

“…Such approaches lack the general applicability of established methods such as CAM-B3LYP, however, and involve extensive choices made between method options and possibly also their parameterisation. More broadly, many asymptotically corrected functionals have now been developed, including recent efforts, 23,36–44 reflecting many and varied design choices. Whilst we consider mostly CAM-B3LYP herein, the elucidated basic principles are expected to be qualitatively representative of all asymptotically corrected functionals.…”

Shedding light on moiré excitons: A first-principles perspective

“…The OT-SRSH functional can reproduce the correct long-range electron-electron and electron-hole interactions in solids by choosing the reasonable parameters. To reduce the computational cost associated with the Fock-like exchange on large systems, we apply first-order perturbation theory to the range-separated hybrid KS (RSH-KS) Hamiltonian and obtain the first order–corrected RSH-KS eigenvalues and eigenfunctions ( 36 , 37 ). We then solve the following non-Hermitian eigenvalue equations of Casida ( 66 ) where the pseudo-eigenvalue ω I is the I th exciton energy level.…”

“…To determine the energies and the many-body wave functions of excitons in MoS 2 /WS 2 heterostructures, we use a recently developed first-principles approach based on the linear-response TDDFT (LR-TDDFT) (41,42), with an optimally tuned, screened, and range-separated hybrid XC functional (OT-SRSH) (43)(44)(45)(46). The method has been implemented in conjunction with plane waves and pseudopotentials to study excitonic properties in semiconductors, including graphene fluoride, phosphorene, and 2D perovskites, and TMD heterostructures (36)(37)(38)(39)(40)64). The OT-SRSH involves the partition of the Coulombic interaction into a short-range and a long-range contribution based on the following expression (65)…”