Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R19: Computational Materials Design and Discovery -- Catalysis and Electronic StructureFocus
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Sponsoring Units: DMP DCOMP Room: BCEC 156C |
Thursday, March 7, 2019 8:00AM - 8:36AM |
R19.00001: Computational design of (electro-)catalysts Invited Speaker: Andrew Peterson Catalysts are crucial in energy conversion technologies, and electrocatalysts directly allow the interconversion of electrical and chemical energy carriers. Here, I will discuss atomistic approaches to describe and design catalyst materials from a computational framework. We have recently developed techniques to control the workfunction (and thus, the potential) of simulations in a "Solvated Jellium" approach. We will show how this allows for the inclusion of reaction barriers and the direct deduction of electrocatalytic mechanisms. We will use this to explain the unique reactivity of Pt that has not been accessible from a traditional "volcano plot" approach, and shed insights for the design of earth-abundant materials with high activities. |
Thursday, March 7, 2019 8:36AM - 8:48AM |
R19.00002: Two-Dimensional Phases of Robust CO2 Reduction Photocatalysts Steven Torrisi, Arunima Singh, Joseph Montoya, Kristin Persson Two-dimensional materials are increasingly popular for applications in catalysis due to useful properties like high surface area, differing surface reactivity from bulk counterparts, and their ability to be formed into nanostructures. This motivates our first-principles based study of the structure and electronic properties of 2D phases of several binary semiconductor materials which have been identified as promising CO2 reduction photocatalysts in the bulk [1]. Using van der Waals corrected functionals as well as HSE06, we identify suitable stable structures with reasonable band gaps for visible light absorption. Finally, we qualitatively evaluate the compounds' catalytic efficiency by computing the adsorption energy of reaction intermediates on each respective surface. |
Thursday, March 7, 2019 8:48AM - 9:00AM |
R19.00003: Computational Dissection of Two-Dimensional Rectangular Titanium Mononitride TiN: Auxetics and Promises for Photocatalysis Liujiang Zhou, Sergei Tretiak Recently, two-dimensional (2D) mateirals with a negative Poisson’s ratios (auxetics) have triggered an enormous interest for their potential applications in the next-generation readable/writeable memory and optoelectronic technologies. Here, by using a broad range of first-principles calculations, we report a systematic study of 2D rectangular materials of titanium mononitride (TiN), exhibiting high energetic and thermal stability due to in-plane d–p orbital hybridization and synergetic out-of-plane electronic delocalization. The rectangular TiN monolayer also possesses enhanced auxeticity and ferroelasticity with an alternating order of Possion’s Ratios, stemming from the competitive interactions of intra- and inter- Ti—N chains. Such TiN nanosystem is a n-type metallic conductor with specific tunable pseudogaps. Halogenation of TiN monolayer downshifts the Fermi level, achieving the optical energy gap up to 1.85 eV for TiNCl(Br) sheet. Overall, observed electronic features suggest that the two materials are potential photocatalysts for water splitting application. |
Thursday, March 7, 2019 9:00AM - 9:12AM |
R19.00004: Exploring PtXnY(2-n) (X, Y= S, Se and Te ; 0≤n≤2) monolayers: Is Janus PtXY the most favorable one? Fatih Ersan, Can Ataca In this study, we investigated Janus and alloy structures of PtXnY(2-n) (X,Y=S,Se,Te; 0≤n≤2) materials on the basis of first-principles plane-wave simulations. Using cluster expansion theory for studying alloys of PtXnY(2-n) monolayers at various concentrations, for half coverage (n=1), our results indicated that Janus type structures are not energetically the most favorable for PtXY monolayers, however they are dynamically and thermally stable. In order to distinguish Janus PtXY structures, we reported the Raman active modes and compared them with bare PtX2 monolayers. Calculated electronic band gap values using hybrid functionals are on-par with available experimental data. It is also reported that spin-orbit coupling significantly modified the electronic band structure of PtXY monolayers. Due to the electronegativity differences of different chalcogen atoms on each surfaces of Janus PtXY structures, the arising dipole moment significantly modified the band alignments on both surfaces. We found that hydrogen evolution and oxygen reduction happen on different surfaces and applied strain enhanced the catalytic activity. Our results indicated that due to their intrinsic dipole moments and band gaps, Janus PtXY monolayers are the perfect candidates for water splitting reactions. |
Thursday, March 7, 2019 9:12AM - 9:24AM |
R19.00005: Computational design of bimetallic core-shell nanoparticles for hot-carrier photocatalysis Luigi Ranno, Stefano Dal Forno, Johannes Lischner Modelling nanoplasmonic devices with tailored properties for photocatalytic, optoelectronic and photovoltaic applications is an important and interesting research field that can lead to groundbreaking technological discoveries. However, developing a quantitative description of nanoplasmonic systems is challenging as quantum-mechanical theories of electrons in large nanoparticles must be combined with nanophotonic approaches. |
Thursday, March 7, 2019 9:24AM - 9:36AM |
R19.00006: Electronic and optical properties of 3d-4d double perovskite Sr2VNbO6: a first-principles DFT+DMFT study Arpita Paul, Turan Birol Double perovskite oxides (A2BB'O6) have drawn enormous interest due to their large variety of emergent properties. We use first-principles DFT+DMFT method to study the electronic and optical properties of Sr2VNbO6, which has both 3d (V) and 4d (Nb) electrons with varying degree of on-site interaction strengths. With both parent compounds SrVO3 and SrNbO3 shown to be promising transparent conductors on the opposite ends of the visible spectrum, we explore the optical properties of the ordered double perovskite Sr2VNbO6. We show that the electronegativity difference and the resulting possibility of charge transfer between the two transition metal cations affect the electronic structure and optical properties such as plasma frequency. |
Thursday, March 7, 2019 9:36AM - 9:48AM |
R19.00007: Combined DFT & STM Study of Fe/Ir(111) Surface States Stephen Gant, Jacob Repicky, Roland Kawakami, Jay A Gupta Chiral spin structures like those present in Fe/Ir(111) are playing an increasingly important role as processor and device size continue to shrink to length scales where quantum effects are relevant. Here, we present density functional theory (DFT) calculations of the Fe/Ir(111) and Ir(111) surfaces and compare them with experimental scanning tunneling microscopy (STM) images and spectroscopy. We performed our calculations using a fully relativistic projector augmented-wave (PAW) approach in conjunction with spin-orbit coupling (SOC) to produce band structures, surface local density of states (LDOS), and simulated STM topography. Experimental STM studies were performed at low temperature in an ultrahigh vacuum environment. Ir(111) was prepared via Ar sputtering, while a monolayer of Fe was deposited in bare Ir(111) via molecular beam epitaxy (MBE). We find good agreement between our DFT calculations and STM data. Of particular interest is the correspondence in Ir(111)’s surface state at the Γ point. Additionally, we present an analysis of how this state is affected by a pseudomorphic monolayer of Fe. |
Thursday, March 7, 2019 9:48AM - 10:00AM |
R19.00008: First-Principles Study of Magnetism in Bilayer Manganese Phthalocyanine Haechan Park, Hai-Ping Cheng, James Nathan Fry, Shuanglong Liu, Yun-Peng Wang
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Thursday, March 7, 2019 10:00AM - 10:12AM |
R19.00009: Contrasting Ferromagnetism in FeS2 Pyrites Induced by Cobalt Doping and by Electrostatic Gating Ezra Day-Roberts, Rafael M Fernandes, Turan Birol Pyrites are a family of transition metal disulfides that host a wide variety of electronic ground states. In particular, the ferromagnetic transition in Co-doped FeS2 has been studied as a source of variable, experimentally accessible electron spin polarizations. Advances in ionic liquid gating have provided an alternative way to change the electron concentration via electrostatic gating instead of chemical doping, thus avoiding the introduction of impurity scattering centers. We use Density Functional Theory combined with a tight-binding model to compare electrostatic gating and chemical doping with cobalt. Using maximally localized Wannier functions to construct a tight-binding model, we calculate the magnetic susceptibility across the entire range of compounds Fe1-xCoxS2. We find that electrostatic gating requires a higher electron concentration than the equivalent in Co-doping to induce ferromagnetism via a Stoner-like mechanism. We attribute this behavior to the formation of a narrow cobalt band near the bottom of the conduction band under doping. This band is not formed for electrostatic gating and wide, low DOS sulfur states are filled instead. |
Thursday, March 7, 2019 10:12AM - 10:24AM |
R19.00010: Ab initio Informed Tight Binding Theory of Axis-dependent Conduction Polarity in Goniopolar Materials Yaxian Wang, Joseph P C Heremans, Joshua E. Goldberger, Wolfgang Windl We have recently shown that NaSn2As2 exhibits opposite conduction polarities along in-plane and cross-plane directions, defined as “goniopolarity”. On the lowest level of theory, we can show that this novel phenomenon originates from a special topology of the Fermi surface, which is essentially determined by the nature of the bonding states in this layered crystal. In this paper, we present an improved fundamental understanding of goniopolarity based on a novel formulation of goniopolarity within the tight-binding model. The tight-binding matrix elements are calculated from GW calculations based on Density Functional Theory (DFT) via maximally localized Wannier functions. Considering a minimum-basis set with sp3 orbitals for both Sn and As, , the 64 hopping integrals are evaluated. Within our model, we provide a new tight-binding based formulation for both Seebeck and Hall coefficients for NaSn2As2 and can show that critical ratios of hopping and on-site matrix elements exist that pose limits for goniopolarity to appear in materials. Based on that, additional candidate materials for goniopolarity can be proposed, and the design space for goniopolar materials in general will be defined. |
Thursday, March 7, 2019 10:24AM - 10:36AM |
R19.00011: Effects of Si Doping on the Electronic Structure and Conductivity of Pure and Off-Stoichiometric Ge2Sb2Te5 Cystrals: First-Principles Investigation Rajarshi Sinha-Roy, Antonin Louiset, Magali Benoit, Lionel Calmels We calculate the electronic structure and electrical conductivity of pure and Si-doped off-stoichiometric Ge2Sb2Te5 cubic crystals, using the relativistic Korringa-Kohn-Rostoker method based on the multiple-scattering theory. These crystals are described by a rock-salt unit cell, in which the chemical disorder is taken into account through the coherent potential approximation. The accuracy of the results is verified by comparing, for several compositions, the density of electronic states calculated with this method and with a method that uses Kohn-Sham wave functions in big supercells. The calculated Bloch spectral function shows the dispersion of the electron states and its modification with the atomic disorder. We show the chemical-composition dependence of the electrical conductivity, and discuss it in terms of the concentration of carriers and of the modification of their scattering by atomic disorder. These results can be used to model Ge-Sb-Te phase-change-material samples, the microstructure of which consists of grains with different compositions, each grain being described by a different value of the conductivity. |
Thursday, March 7, 2019 10:36AM - 10:48AM |
R19.00012: Electrical Conductivity of Graphene-Polymer Composite Foam Zilu Wang, Adamson H Douglas, Andrey Dobrynin Graphene-polymer composites have potential applications in energy storage, oil absorption, and sensing. Here, we focus on dependence of the electrical conductivity of the composite graphene-polymer foams as a function of their composition and deformation. Using a combination of the coarse-grained simulations and analytical calculations we developed a bottom-up approach which allows us to express the macroscopic sample conductivity in terms of conductivity of the graphene layers coating the foam’s shells. In particular, we propose a close packing shell model to describe the conductivity of the graphene shells with multiple contact points. This shell conductivity model is used to calculate the change in foam conductivity upon deformation which could be induced either by solvent absorption or by external foam compression/elongation. The model predictions are compared with the experimental data on conductivity of composite poly(butyl acrylate)/graphene foams. |
Thursday, March 7, 2019 10:48AM - 11:00AM |
R19.00013: Density matrix renormalization group study of Hubbard ladders Yilin Zhao, Ling Wang, Gayanath Fernando Motivated by exact diagonalization work on small Hubbard clusters1, we focus on Hubbard ladder systems using the DMRG method. The exact diagonalization work has yielded an extremely rich variety of results related to the physics of the minimal orbital Hubbard clusters and the present study will attempt to elucidate related size and other effects. |
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