Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Q59: First-Principles Simulations of Excited-State Phenomena: ApplicationsFocus
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Sponsoring Units: DCOMP Chair: Volodymyr Turkowski, University of Central Florida; Carsten Ullrich, University of Missouri Room: Room 301 |
Wednesday, March 8, 2023 3:00PM - 3:36PM |
Q59.00001: Effects of strong electron-electron correlations and memory in materials and time-dependent density-functional theory: recent progress and challenges Invited Speaker: Volodymyr Turkowski Charge correlations play an important role in the static and dynamical properties of many materials, for example in the optical response of systems excited by short laser pulses. Because of the involvement of a number of atomistic processes that define the response of the system, ab initio tools are needed to characterize them. Time-Dependent Density-Functional Theory (TDDFT) is an excellent choice, provided one has an appropriate exchange-correlation (XC) potential that accurately accounts for electron-electron and other charge correlations. Until very recent years, such potentials were not available. In this presentation, we first summarize our TDDFT approach for strongly correlated materials [1], in which a nonadiabatic XC potential is derived from the charge susceptibility (linear response) and electron self-energy (nonlinear response) obtained from the Dynamical Mean-Field Theory solution of an effective Hubbard model. We present results of application of the approach to types of materials: Mott insulators and a transition metal. We demonstrate how the effects of charge correlations and memory are revealed in the nonhomogeneous ultrafast metallization of VO2,[2] demagnetization of Ni [1] and melting of the antiferromagnetic order in V2O3. We discuss how these ultrafast processes reveal themselves in the emission spectra of the materials and the challenges that lie ahead for the treatment of strong perturbations. |
Wednesday, March 8, 2023 3:36PM - 3:48PM |
Q59.00002: Photoexcitations and optical response of carrier-doped monolayer transition metal dichalcogenides and heterostructures from first principles Aurelie Champagne, Jonah B Haber, Supavit Pokawanvit, Olugbenga M Adeniran, Zhenfei Liu, Diana Y Qiu, Felipe H da Jornada, Jeffrey B Neaton The optoelectronic properties of 2D semiconductors are highly sensitive to the surrounding dielectric environment, a direct result of intrinsic weak and highly non-local dielectric screening. Less studied is the role of free carrier density on those properties. While the ab initio GW plus BSE approach is the state-of-the-art method for the accurate prediction of one and two particle excitations, respectively, the BSE is typically solved in the static limit, acceptable if the exciton binding energy is much smaller than the plasma frequency, but inadequate for systems with finite carrier density displaying acoustic carrier plasmon energies below or nearly resonant with the exciton binding energy. We develop a plasmon-pole model that captures dynamical screening associated with free carriers and local-field effects. We apply this approach to study the doping-dependence of the QP and optical properties of a monolayer MoTe2 and of organic-TMD bilayer interfaces. For the former, we predict a QP band gap renormalization of several hundreds meV, and a similar decrease in the exciton binding energy. For the interface, we predict a transition from type-I to type-II interface and the emergence of new interlayer excitons, resulting from an interplay between charge carrier screening and substrate screening. |
Wednesday, March 8, 2023 3:48PM - 4:00PM |
Q59.00003: Giant bulk photovoltaic effect driven by the wall-to-wall charge shift in WS2 nanotubes Bumseop Kim, Noejung Park, Jeongwoo Kim Photo-induced quantum phenomena observed in two-dimensional transition metal dichalcogenides (TMDs) have attracted substantial scientific interest, which is to be combined with novel opportunities in future for advanced optoelectronic devices [1, 2]. Among the family of TMDs, the one-dimensional nanotube is particularly attractive because it produces a spontaneous photocurrent which is absent in its higher-dimensional counterparts [3]. We present that TMD nanotubes provide a giant shift current near the infrared region, which amounts to four times the value previously reported in the higher frequency range [4]. The key geometrical advantage is ascribable to the wall-to-wall charge shift, and we consider a Janus-type heteroatomic configuration as an example that maximizes such advantage. To go beyond the perturbative treatment of the electronic states near the ground states, we carried out the real-time integration of the photoinduced current using time-dependent density functional theory, which can take the full nonlinear effect of strong fields into account. Our findings can lead to new avenues for low-dimensional optoelectronic devices and provide a solid basis for a complete quantum mechanical understanding of the unique light–matter interaction rooted in the geometric characteristics of the reduced dimension. |
Wednesday, March 8, 2023 4:00PM - 4:12PM |
Q59.00004: Transferability of Screened Range-Separated Hybrid Functionals for Layered Materials Maria Camarasa Gomez, Ashwin Ramasubramaniam, Jeffrey B Neaton, Leeor Kronik The accurate description of electronic and optical properties is a long-standing challenge in density functional theory. Screened range-separated hybrid (SRSH) functionals have been successfully employed for the determination of gap energies and optical spectra in solids [1, 2]. Generally, the range-separation parameter and fraction of short-range exact exchange that define the SRSH are material- and structure-dependent, raising the question of transferability between 2D and bulk phases of layered materials. Following [3], we explore 2D and bulk phases of various layered materials. We show that systematic determination of SRSH parameters that simultaneously describe different structural phases of the material with quantitative accuracy is possible. |
Wednesday, March 8, 2023 4:12PM - 4:24PM |
Q59.00005: Accurate band gaps and optical spectra of halides and oxides from a non-empirical, localization based optimal tuning of a screened range-separated hybrid functional Guy Ohad, Stephen E Gant, Dahvyd Wing, Jonah B Haber, Maria Camarasa Gomez, Ayala V Cohen, Francisca Sagredo, Ashwin Ramasubramaniam, Marina R Filip, Jeffery B Neaton, Leeor Kronik Accurate prediction of fundamental band gaps of crystalline solid-state systems, entirely within density functional theory, has been a long-standing challenge. Previously, we developed a simple and inexpensive method that achieves this by means of nonempirical optimal tuning of the parameters of a screened range-separated hybrid functional [1]. The tuning involves the enforcement of an ansatz that generalizes the ionization potential theorem to the removal of an electron from an occupied state described by a localized Wannier function in a modestly sized supercell calculation. Here we present applications of the method to more complex systems, notably halide perovskites and metal oxides. We demonstrate quantitative accuracy in band gaps and optical absorption spectra with respect to experiment and a comparable level of accuracy to many-body perturbation theory calculations. We further demonstrate the merit of using the optimally tuned eigensystem as a starting point in combined GW plus Bethe-Salpeter calculations. |
Wednesday, March 8, 2023 4:24PM - 4:36PM |
Q59.00006: Investigation of inverse photoemission and field-assisted radiative electron capture in semiconductor nanoparticles Arindam Chakraborty, Nicole Spanadda, Kevin Mesta This work presents a theoretical and computational investigation of the electron affinities, electron-capture cross-sections, inverse photoemission energies, and inverse photoemission cross-sections for a series of PbS, PbSe, CdS, and CdSe quantum dots. Inverse photoemission occurs when an incident electron is captured by a material in one of the high energy unoccupied states which then subsequently de-excites to the lowest unoccupied molecular orbital (LUMO) state by emitting a photon. Using the kinetic energy of the captured electron and the energy of the generated photon, one can back-calculate the information about the unoccupied states. Inverse photoemission allows for direct spectroscopic investigation of the conduction band and is used in surface characterization of solids. This theoretical and computational study uses diagrammatic time-dependent many-body perturbation theory and 1-particle Green's function method to calculate the electron capture cross-section, photon emission oscillator strength, and the overall inverse photoemission cross-section in quantum dots. The results from this study show that the quantities related to the electron capture process and the photoemission process follow different size-dependent scaling laws with respect to increasing dot size. To enhance the inverse photoemission process, we demonstrate that the overall radiative electron capture cross section of quantum dots can be significantly increased by application of external electric field. |
Wednesday, March 8, 2023 4:36PM - 4:48PM |
Q59.00007: Photoluminescence and DFT simulation of conductivity of the p-type doped and charge-injected cis-polyacetylene of Cis-Polyacetylene Semiconductor Material KAMRUN NAHAR KEYA, Wenjie Xia, Dmitri Kilin Photoluminescence (PL) is one of the key observables in experimental characterizations of optoelectronic materials, including conjugated polymers (CPs). Due to their tunable electronic and optical properties, semiconducting CPs have shown great potential in organic solar cells and organic field-effect transistors (OFETs). A simplified model of cis-PA oligomer is used to explain the mechanism of PL of the CPs. We explore the phonon-induced relaxation of the excited states. Here, the dissipative Redfield equation was used with the nonadiabatic couplings as parameters. The relaxation rate of the electron is found to be faster than the relaxation rate of the hole. The dissipative excited-state dynamics were combined with radiative recombination channels to predict the PL spectrum. The simulation revealed similarities in the absorption and emission spectra. The main result is that the computed PL spectrum demonstrates two mechanisms of light emission originating from (i) the inter-band transitions, corresponding to the same range of transition energies as the absorption spectrum, and (ii) intra-band transitions not available in the absorption spectra. [1] The results can be used for improving organic semiconductor materials for photovoltaic and LED applications. Results on single oligomer serve as a basis for the computational predictions of electronic and optical properties of ensembles of cis-PA multiple oligomers in two different forms (a) undoped cis-PA and (b) cis-PA doped by phosphorous fluoride via DFT with hybrid functionals. The comparison of undoped cis-PA under the constraint of injected charge carrier and cis-PA doped by phosphorous fluoride shows that either doping or injection provides very similar features in electronic structure, optical properties, and conductivity. [2] These observations provide a better understanding and practical use of the properties of polyacetylene films for flexible electronic applications. |
Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q59.00008: Optical properties of anisotropic CdSe nanocrystals from first principles Erick I Hernandez Alvarez, Xiangrui Deng, Andrew M Smith, Andre Schleife CdSe nanocrystals are popular light-emitting materials for optoelectronic devices and bioimaging applications. In contrast to zero-dimensional (0D) quantum dots, 1D nanorods and 2D nanoplatelets can have narrower emission bandwidths and anisotropic photophysical properties. |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q59.00009: Understanding the effect of ligand exchange in CdS quantum dots from many-body perturbation theory Sandip Aryal, Joseph Frimpong, Zhenfei Liu CdS quantum dots (QDs) are often synthesized with ligands binding to different facets of the QDs to passivate and eliminate the dangling bonds on the QD surface. A typical procedure used in the fabrication of CdS QDs is ligand exchange, replacing bulky ligands such as oleic acid with compact ones such as thioglycolic acid. However, a quantitative understanding of the effect of the ligand exchange on the electronic and optical properties of the CdS QDs is missing, which could impede an accurate determination of the QD size experimentally, where an empirical relationship between the QD size and the optical excitation is often used. In this work, we model various interfaces formed between the two ligands and different facets of CdS QD and employ the first-principles GW-BSE method to investigate how the ligand exchange quantitatively modulates the quasiparticle and optical properties of the CdS QD. Our results indicate that the ligand effects need to be taken into account in the experimental determination of the QD size. |
Wednesday, March 8, 2023 5:12PM - 5:24PM |
Q59.00010: Effect of Polaron Formation on Carrier Transport Properties of Transition Metal Oxides Andrew Grieder, Mingpeng Chen, Tyler J Smart, Kiley Mayford, Samuel Mcnair, Anica Pinongcos, Sam Eisenberg, Frank G Bridges, Yat Li, Yuan Ping Transition metal oxides (TMO) are promising candidates for materials in energy conversion and storage applications. However, due to formation of small polarons, low electrical conductivity has been the major bottleneck for its practical applications. Atomic doping has been shown as an effective approach to improve their electrical conductivity, but a detailed mechanistic understanding is still needed and important for experimental synthesis of ideal materials. Since atomic doping affects both carrier concentration and carrier mobility, they are both important for understanding dopant effects on electrical conductivity. Using hematite as a prototypical TMO, we have shown an accurate prediction of carrier concentration through our recently developed method of calculating carrier concentration based on charge neutrality condition, and prediction of polaron mobility of doped systems through combining generalized Landau-Zener theory with kinetic Monte-Carlo sampling. With both quantities, we then calculated carrier conductivity in good agreement with experiments. |
Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q59.00011: Towards accurate excitation energies in supramolecular systems: combining T-CDFT and fragments in the BigDFT code Martina Stella, Luigi Genovese, William Dawson, Laura Ratcliff Despite the variety of available computational approaches, state-of-the-art methods for calculating excitation energies such as time-dependent density functional theory (TDDFT), are typically computationally demanding and thus limited to moderate system sizes. Thanks to a new variation of constrained DFT (CDFT), implemented in the BigDFT code and recently published by our group, we have shown to be able to robustly model both local and charge-transfer excitation energies with a comparable precision to TDDFT for local excitations, while not exhibiting the typical limits of standard TDDFT for charge-transfer states, for a computational cost close to ΔSCF. As T-CDFT is implemented within the linear scaing formalism it is naturally suited to be paired with the fragment approach already availalbe in the BigDFT code. By properly combining these two infrastructures, one can use TCDFT to impose excitations on particular fragments in supramolecular systems. In the example of local excitations on a molecule (fragment) in a given environment, where no strong coupling with the environment is expected, the constraint could be imposed between orbitals associated with the target fragment only, while still treating the full system at DFT level. In this talk I will show how this approach allows the exploration of explicit environment effects on excitation energies in systems such as TADF materials, paving the way for future simulations of excited states in realistic morphologies. |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q59.00012: Predictions of Plasmonic Hot Carrier Energies Using Machine Learning Adela Habib, Ben T Nebgen, Nicholas E Lubbers, Sergei Tretiak Atomistic simulation of electron dynamics using machine learning provides a pathway to scale computational studies from a few 10s of atoms to device levels with 1000s of atoms, thereby facilitating efficient device design. For example, studies of plasmonic hot carrier-based devices for efficient energy-harvesting has been limited to small scale systems because of the prohibitively expensive quantum-mechanical simulation methods such as nonadiabatic molecular dynamics (NAMD) or real-time time-dependent density functional theory (rt-TDDFT). On the other hand, we have shown that atomistic neural networks (NN) architectures can estimate a time dependent electron density capable of capturing plasmon formation and its subsequent decay into hot carriers, in nanostructures of 500+ atoms, at fractions of the quantum-mechanical simulation time and with minimal quantum-mechanical input data. In this talk, I will present the extension of this work, showing machine-learned hot carriers’ distributions evolving over time as functions of their energy. These predictions enable extraction of useful insights such as identifying hot-spots for enhancing plasmon-driven photocatalytic reactions in a metal and molecule adsorbate system. Our goal is to explore the transferability of our workflow in pursuit of a scheme for affordable modeling of hot carrier dynamics in systems with thousands of atoms. |
Wednesday, March 8, 2023 5:48PM - 6:00PM |
Q59.00013: Role of oxygen vacancy in α-Al2O3 near-surface: A first-principles based approach to study the hydration of surface Vijaya Begum-Hudde, Barbara Jones, Andre Schleife The α-Al2O3 surface is a widely studied system as it hosts a range of important technological applications such as catalysis, and natural occurring processes such as corrosion. Oxygen vacancies near the surface of α-Al2O3 (0001) are of significant interest as they aid in understanding the hydration of the surface which is critical to the aforementioned processes. Employing first-principles calculations, we investigated the α-Al2O3 (0001) surface with Al-termination to study the surface effects on electronic and structural properties. Starting with the PBEsol exchange-correlation functional to relax the atomic positions, we observe a decrease in the direct band gap from 5.98 eV (bulk) to 4.90 eV (surface), accompanied by the reconstruction of the surface Al ions. The vertical relaxation is maximum for the surface Al layer (inwards by ~88% of the unrelaxed configuration) wherein the Al ions are almost in the same layer as the subsequent O layer, and the displacements of the subsequent layers are concurrent with previous density-functional theory studies and experimental results from X-ray diffraction. Upon introducing the O-defect, a further reduction in the band gap and emergence of defect levels is observed. These defect states are characterized to describe an active space for a subsequent quantum embedding approach. |
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