LCAO-TDDFT-k- ω : spectroscopy in the optical limit

Abstract

Understanding, optimizing, and controlling the optical absorption process, exciton gemination, and electron-hole separation and conduction in low dimensional systems is a fundamental problem in materials science. However, robust and efficient methods capable of modelling the optical absorbance of low dimensional macromolecular systems and providing physical insight into the processes involved have remained elusive. We employ a highly efficient linear combination of atomic orbitals (LCAOs) representation of the Kohn-Sham (KS) orbitals within time dependent density functional theory (TDDFT) in the reciprocal space (k) and frequency (ω) domains, as implemented within our LCAO-TDDFT-k-ω code, applying either a priori or a posteriori the derivative discontinuity correction of the exchange functional Δ x to the KS eigenenergies as a scissors operator. In so doing we are able to provide a semi-quantitative description of the photoabsorption cross section, conductivity, and dielectric function for prototypical 0D, 1D, 2D, and 3D systems within the optical limit ( q → 0 + ) as compared to both available measurements and from solving the Bethe-Salpeter equation with quasiparticle G 0 W 0 eigenvalues (G 0 W 0 -BSE). Specifically, we consider 0D fullerene (C 60 ), 1D metallic (10, 0) and semiconducting (10, 10) single-walled carbon nanotubes, 2D graphene (Gr) and phosphorene (Pn), and 3D rutile (R-TiO 2 ) and anatase (A-TiO 2 ). For each system, we also employ the spatially and energetically resolved electron-hole spectral density to provide direct physical insight into the nature of their optical excitations. These results demonstrate the reliability, applicability, efficiency, and robustness of our LCAO-TDDFT-k-ω code, and open the pathway to the computational design of macromolecular systems for optoelectronic, photovoltaic, and photocatalytic applications in silico.

Systematic competition between strain and electric field stimuli in tuning EELS of phosphorene

“…On the other hand, the high-energy interband transitions correspond to the ZZ direction, while the low-energy ones belong to the AC direction. These all are in an excellent agreement with recent measurements 72 – 74 .…”

Ab initio study of electromagnatic modes in two-dimensional semiconductors: Application to doped phosphorene

“…This value underestimates the theoretical results ∆ ∼ 0.6 − 0.8eV reported in Refs. [28][29][30][31][32][33] as well as experimental reults ∆ ∼ 0.9eV reported in Refs. [35,36,38].…”

“…The optical properties and dielectric response of phosphorene have been systematically investigated [8,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. For instance, the intensities and tuning of hyperbolic plasmons in supported or self-standing phosphorene were explored by using different models for the optical conductivity, either via tight binding approximation (TBA) fitted to density functional theory (DFT) calculations or via GW methods [8,19,21].…”

“…Besides the hyperbolic plasmon, phosphorene shows very interesting excitonic effects. Sophisticated GW-BSE calculations of the quasi-particle band gap and exciton binding energies as a function of strain, polarisation, and dielectric environment were studied in phosphorene [28][29][30][31][32][33]. Moreover, the excitonic fine structure in monolayer and few-layer black phosphorus were studied through reflection and photoluminescence excitation measurements [35].…”

Strain engineering of hyperbolic plasmons in monolayer carbon phosphide: a first-principles study

“…Overall, the optical response of 2D materials, including the in-plane conductivity and polarizability, strats by calculating the non-interacting density-density response function 83,84 in wave-vector space and frequency domains; (, ω ). After determining the linear response within the random phase approximation (RPA), by working in the optical limit (), the optical conductivity tensors can be described by the polarizability tensor: , 85 where α ( ω ) is the polarizability. 85 A dense sampling of k wave vectors was used by employing a 266 × 430 × 1 Monkhorst–Pack k -mesh 79 and a Lorentzian broadening parameter of η = 25 meV was assumed.…”