Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E22: First-Principles Modeling of Excited-State Phenomena in Materials III: Low-Dimensional Materials and Organic CrystalsFocus Live
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Sponsoring Units: DCOMP DCP DMP Chair: Feliciano Giustino, University of Texas at Austin |
Tuesday, March 16, 2021 8:00AM - 8:36AM Live |
E22.00001: First-principles studies of light-matter interactions in two-dimensional structures Invited Speaker: Li Yang I will beging with an introduction of light-matter interactions and excited states, such as quasiparticles and excitons, and how to calculate them by first-principles many-body perturbation theory. Then I will focus on simulations of light-matter interactions of emerging two-dimensional (2D) anisotropic black phosphorus and magnetic materials. By calculating electron-electron and electron-hole interactions, we can predict and explain important measurements. Finally, I will go beyond linear light-matter interactions and propose enhanced charge and spin photocurrents in layered magnetic axion insulators and non-centrosymmetric semiconductors, giving hope to realizing light-driven pure spin current. |
Tuesday, March 16, 2021 8:36AM - 8:48AM Live |
E22.00002: Excited-state propagation and radiative lifetimes from exciton dispersion Sivan Refaely-Abramson, Galit Cohen, Dana Novichkova, Diana Qiu Understanding the energetics and dynamics of excited states formed by light-matter interactions is essential for applications across optoelectronics and photophysics. In particular, exciton evolution and decay lifetimes are coupled to optical selection rules, resulting from the atomic structure of the host materials. In this work, we study exciton time propagation and its relation to material structure and dimensionality from ab initio GW-BSE-based computations. We examine four representative systems: solid pentacene, an organic molecular crystal with large excitonic effects; monolayer MoS2, with degenerate excitons in different momentum-space valleys; monolayer black phosphorus, a material exhibiting linear dichroism; and (8,0) single-walled carbon nanotube, a prototypical quasi-1D system. We explore how features of the exciton bandstructure manifest in its time-evolution, evaluate the associated exciton radiative lifetime and investigate thermalization effects. |
Tuesday, March 16, 2021 8:48AM - 9:00AM Live |
E22.00003: Tunable edge states of nanoribbons by density functional theory and GW approximations Hong Tang, Bimal Neupane, Adrienn Ruzsinszky 2D layered materials belong to a rapidly growing area in material science and technology, due to their amazing properties and promising applications in fields of energy recovery,storage, catalysts, next-generation electronics, optoelectronics. Their properties are tunable via configurations, strain, and bending. Previous studies [1,2] by PBE and SCAN functionals showed that under mechanical bending, some TMD monolayer nanoribbons undergo high nonuniform local strain within the curved layers, much larger than uni-axial strain, making band edge states more tunable in these 2D materials. It helps to remove the strong Fermi-level pinning in the flat states, making the materials usable in contact-engineering [1,2]. Many-body GW approximations can provide accurate band structures for solid materials. We use GW calculations to check the tunability of the band edges of MoS2 nanoribbon with various widths. To make the GW computation manageable, the static Coulomb-hole remainder correction will be considered. The results will be compared with that from modified meta-GGA semilocal density functionals. |
Tuesday, March 16, 2021 9:00AM - 9:12AM Live |
E22.00004: Effect of stacking orientation on the electronic and optical properties of polar 2D III-nitride bilayers Nocona Sanders, Mingfei Zhang, Kelsey Mengle, Liang Qi, Emmanouil Kioupakis Given the successful synthesis of 2D GaN and investigations into the properties of freestanding 2D nitrides, bilayers of these materials are now of particular interest. Extreme quantum confinement is a viable method to shift light emission to shorter wavelengths, but in 2D nitrides this is counteracted by the quantum-confined Stark shift due to the strong inherent polarization perpendicular to the 2D plane. We report the electronic and optical properties of 2D BN, GaN, AlN, and InN in various stacking orientations, such that the electric fields are either aligned or anti-parallel in two possible configurations. We employ density functional theory and quasiparticle corrections with the GW method, as well as the Bethe-Salpeter Equation, to derive accurate band structures, exciton binding energies, and luminescence energies. Our results demonstrate that the stacking orientation acts as a degree of freedom to tune the band gap of polar 2D bilayers over several eV, as well as to control the direct or interlayer nature of excitons, giving critical insight in how to improve 2D III-nitride-based optoelectronics. |
Tuesday, March 16, 2021 9:12AM - 9:24AM Live |
E22.00005: Exciton diffusion in organic crystals from first principles many-body perturbation theory Jonah Haber, Felipe Da Jornada, Sivan Refaely-Abramson, Gabriel Antonius, Steven G Louie, Jeffrey Neaton Molecular crystals are attractive candidates for solar energy conversion applications due to their strong light-matter interactions, large structural tunability, and the relative inexpense with which they can be synthesized and processed. In organic semiconductors, an important step in the energy conversion process is the diffusion of a photo-excited exciton to a donor-acceptor interface where charge separation of the strongly-bound electron-hole pair may occur. In this talk, we present a framework, based on ab initio density functional perturbation theory and many-body perturbation theory within the GW plus Bethe-Salpeter equation approach, for computing the rate of exciton diffusion in organic crystals. We apply our approach to select members of the oligoacene family. Through our analysis we build microscopic insight into which lattice vibrations are most important for exciton transport and how the spin state of the exciton affects the diffusion rate. |
Tuesday, March 16, 2021 9:24AM - 9:36AM Live |
E22.00006: Quasiparticle electronic structure of phthalocyanine-transition metal dichalcogenide interfaces from first-principles GW Olugbenga Adeniran, Zhenfei Liu Two-dimensional transition-metal dichalcogenide (TMD) nanostructures have attracted much attention because of their appealing optoelectronic properties. Modulation of these materials is crucial in tuning their properties and consequently widening their applications. Herein, we investigate the modulation of the electronic structure of TMDs by (metallo)phthalocyanine molecules, using first-principles GW. We apply the substrate screening and dielectric embedding approaches to expedite the calculation, and examine the many-body dielectric screening at such molecule-semiconductor interfaces. We show how the gaps of the phthalocyanine molecules and the band structures of TMDs are altered upon formation of the interface. We carefully compare different GW approaches for the heterogeneous interface, for the purpose of method development. Moreover, our calculations provide benchmark results in the quasiparticle energy level alignment at the interface, as well as trends for a series of metallophthalocyanine molecules and TMD substrates. We provide theoretical insight into a few existing experiments and discuss implications of our results. |
Tuesday, March 16, 2021 9:36AM - 9:48AM Live |
E22.00007: Optical Properties of Wurtzite CdSe Nanorods from First Principles Simulations Erick Ivan Hernandez Alvarez, Sung Jun Lim, Andrew Michael Smith, Andre Schleife The tunability of optical properties of colloidal semiconductor nanocrystals by size, shape, and composition make them attractive for applications ranging from bioimaging to solar energy conversion. Growth conditions can be tuned to yield anisotropic nanorods with one-dimensional quantum confinement and controllable thickness, length, and aspect ratios. These structural parameters together enable precise control over spectroscopic properties. With empirical lengths typically between 5–100 nm, calculating the ground state electronic properties of nanorods is prohibitively expensive with current implementations of density functional theory (DFT) due to the large system size and a lack of periodic boundary conditions. In contrast, nanowires can be described with periodic boundary conditions in the axial direction, enabling calculation of electronic properties using a small unit cell. We use DFT to compute the ground state electronic structure and simulate the optical properties of wurtzite CdSe nanowires with varying wire thickness. We compare calculated nanowire spectra with experimental spectra of nanorods with similar thicknesses but different aspect ratios at the band edge to understand how thickness and aspect ratio independently affect nanorod optical properties. |
Tuesday, March 16, 2021 9:48AM - 10:00AM Live |
E22.00008: Charge-transfer excitons in atomically thin GaN quantum wells Woncheol Lee, Mackillo Kira, Emmanouil Kioupakis We investigate the properties of spatially indirect excitons (IXs) confined in pairs of atomically thin GaN wells, separated by polar AlN barriers. Atomically thin GaN is a promising material for realizing strongly bound excitons because of its extreme quantum confinement effect. Also, the spontaneous polarization fields in nitride heterostructures allow IXs to form in atomically thin GaN quantum wells even without external electric fields. We show that the overlap of the electron and hole wavefunctions, the degree of electron-hole interaction, and the character (IX or DX) of the lowest-energy exciton can be controlled by changing the thickness and the resulting electrical polarization of the separating AlN barrier. We demonstrate that room-temperature stable IXs, with radiative decay rates several orders of magnitude lower than DXs, can be realized in these atomically thin polar nitride heterostructures for potential excitonic applications at room temperature based on a commercial semiconductor platform. |
Tuesday, March 16, 2021 10:00AM - 10:12AM Live |
E22.00009: Pyrene-Stabilized Acenes as Intermolecular Singlet Fission Candidates: Importance of Exciton Wave-Function Convergence Xingyu Alfred Liu, Rithwik Tom, Xiaopeng Wang, Bohdan Schatschneider, Noa Marom
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Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E22.00010: Quasiparticle electronic structure of 2D heterotriangulene-based covalent organic frameworks and their interfaces with Au (111) surface JOSEPH FRIMPONG, Zhenfei Liu As the search for better materials with new functionalities continues, accurate determination of the bandgaps of materials and energy level alignments at interfaces is central to rational materials design. In this work, we employ the first-principles GW approach to accurately determine the quasiparticle electronic structure of a series of 2D carbonyl bridged heterotriangulene-based covalent organic frameworks (COFs) featuring kagome lattice, with their properties ranging from a semi-metal to a wide-gap semiconductor. Moreover, we study the adsorption of these COFs on Au (111) surface and characterize the interfacial energy level alignment. To reduce the computational cost, we apply the dielectric embedding GW approach and show that it leads to close agreement with experiment. In addition to the well-studied gap renormalization of adsorbates, our calculations illustrate how the interfacial dielectric screening effect modulates the structure of the kagome bands, the charge-carrier mobilities of semiconducting COFs, as well as the Fermi velocity of the semi-metallic COF. Our study provides benchmark results for future experimental and computational work and novel insight into materials design. |
Tuesday, March 16, 2021 10:24AM - 10:36AM Live |
E22.00011: Trion induced photoluminescence and brightening of intervalley excitons in a doped MoS2 monolayer Vasili Perebeinos, Yaroslav Zhumagulov, Dmitry R. Gulevich, Alexei Vagov, Paulo E. Faria Junior Transition metal dichalcogenide monolayers are direct bandgap semiconductors with the rich interplay of the valley and spin degrees of freedom. Strong Coulomb interaction leads to tightly bound excitons and trions, a quasiparticle composed of two electrons and a hole. We report Bethe-Salpeter equation solution for the three-particle wavefunction in the basis set of model Hamiltonian for single particles. The calculated absorption [1] and photoluminescence [2] spectra as a function of doping and temperature reproduce existing experimental data in MoS2 monolayer and predict novel spectroscopic features due to the brightening of the intervalley excitons at finite doping. |
Tuesday, March 16, 2021 10:36AM - 10:48AM Not Participating |
E22.00012: Fundamental Gap of Fluorographene by Many-Body GW and Diffusion Quantum Monte Carlo Methods Matus Dubecky, Frantisek Karlicky, Stanislav Minarik, Lubos Mitas Fluorographene (FG) is a promising large band gap graphene-derivative. Predictions of its fundamental gap (Δ) vs experiments vary rather significantly. We present benchmark Δ for FG from large-scale many-body GW and fixed-node diffusion Monte Carlo (FNDMC) computations. Both approaches arrive at Δ≈7.1±0.1 eV. Second part presents a possibility to compute Δ from neutral energy differences within 1-determinant Bloch-orbital-based FNDMC. We argue, why instead of the expected optical gap, such an approach results in energy differences that do not account for an electron-hole interaction and nominally correspond to Δ in the thermodynamic limit. Conditions when this case actually applies are outlined as well. |
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