Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P20: First-principles Modeling of Excited-state Phenomena in Materials IX: Applications of First Principles Methods to Magnetic and Catalytic MaterialsFocus
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Sponsoring Units: DCOMP DMP GMAG Chair: David Strubbe, University of California, Merced Room: BCEC 157A |
Wednesday, March 6, 2019 2:30PM - 3:06PM |
P20.00001: Charge separation and band alignment at photo-electrochemical interfaces Invited Speaker: Ismaila Dabo Solar energy is the most abundant energy source available to humankind, but this energy cannot be harnessed on demand due to the variability of sunlight. Artificial photosynthesis overcomes that variability through the direct photocatalytic storage of solar power into chemical fuels. Nevertheless, most of the stable photocatalysts in use today rely on metal oxide semiconductors whose bandgap does not match the solar spectrum. This presentation will discuss the development and experimental validation of computational protocols to understand, predict, and optimize visible-light-active materials that can split water into hydrogen and oxygen with a focus on answering the critical questions that surround (1) solar compatibility using electronic-structure methods beyond density-functional theory, (2) electrochemical stability by exploiting quantum-continuum embedding methods, and (3) band-edge alignment by means of machine-learning statistical techniques. |
Wednesday, March 6, 2019 3:06PM - 3:18PM |
P20.00002: Ground and excited states of iron-phthalocyanine: a DFT+DMFT analysis Volodymyr Turkowski, Shree Ram Acharya, Carlos Garcia-Fernandez, Nicolas Lorente, Talat S. Rahman Although the iron-phthalocyanine (FePc) molecule has been the subject of numerous experimental and theoretical studies, questions still remain about its ground and excited states. We have performed a Density Functional Theory+Dynamical Mean-Field Theory (DFT+DMFT) analysis of the spin resolved density of states of this interesting molecule to show that local dynamical effects (time-resolved on-site electron-electon interactions), which are inherently taken into account within DMFT, modify the DFT and DFT+U electronic spectrum of the molecule in the following way: they shift energy of a number of levels (most notably in the HOMO-LUMO energy range) and lead to new peaks. Such a modification may help resolve the issue of the ground state of FePc (complicated by the competing close-in-energy configurations) and can dramatically affect the transport, electronic and other propertiers of the molecule. Though further experimental test of the results are needed to quantify the accuracy of the DMFT approach for nanoscale systems, our results suggest that similar to extended systems time-resolved on-site electron-electron interactions play an important role in molecules that contain transition-metal atoms. |
Wednesday, March 6, 2019 3:18PM - 3:30PM |
P20.00003: Electron-phonon coupling in photoexcited Bi2Te3 Jose Querales-Flores, Ivana Savic, Éamonn Murray, Stephen B Fahy, Jonathan Sobota, Samuel W Teitelbaum, Takahiro Sato, Matthieu Chollet, James M Glownia, Mariano Trigo, Trevor P Bailey, Ctirad Uher, Patrick S Kirchmann, Zhi-Xun Shen, Costel R. Rotundu, Thomas Henighan, David A Reis
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Wednesday, March 6, 2019 3:30PM - 3:42PM |
P20.00004: Calculation of excitation energies using locally-projected real-space geminal screened electron-hole interaction kernel Peter McLaughlin, Arindam Chakraborty The geminal-screened electron-hole interaction kernel (GSIK) is a real-space representation for describing electron-hole correlation in charge-neutral excitations. Unlike MBPT and EOM methods, the GSIK method avoids using virtual or unoccupied orbitals for constructing electron-hole interaction kernel. This feature allows GSIK method to be used for chemical systems where inclusion of a large number of unoccupied orbitals will be computationally prohibitive. This talk will present the locally-projected formulation of the GSIK method where the electron-hole interaction kernel is calculated using an atom-in-cluster approach. It will be demonstrated that the local-projection allows the evaluation of the kernel to be performed at a linear-scaling cost. The locally-projected GISK method was applied to large metallic (Au300) and semiconductor (Pb150S150) nanocluster for calculation of optical gap and electron-hole binding energies. The results from these calculations demonstrate the efficacy of the GSIK method for capturing electron-hole correlation in large clusters and nanoparticles. |
Wednesday, March 6, 2019 3:42PM - 3:54PM |
P20.00005: Structural parameters governing excited-state properties of self-assembling π-conjugated peptides: a classical and quantum study Bryce Thurston, Ethan Shapera, Andre Schleife, Andrew L Ferguson Peptides that self-assemble are of significant interest for use in the fabrication of biocompatible nano-aggregates. Non-natural π-conjugated subunits may be embedded into the peptide backbone, leading resulting β-sheet-like ribbons formed from self-assembly to have electronic and photophysical properties. Alteration of the amino acid composition of the peptides can have a significant impact on the measured absorption spectra of aggregates, but the exact geometric origin of these changes is unknown. In order to probe these composition-induced alterations, we utilize time-dependent density functional theory calculations to study the excited state properties of peptide configurations extracted from molecular dynamics simulations. We identify geometric variables describing π-conjugated core geometries that appear to be determinative of the wavelength at which the absorption spectrum reaches its peak. When applied to MD simulations, the resulting regression model is shown to be in qualitative agreement with experiment, laying the foundation for in silico prediction of absorption properties of peptide aggregates. |
Wednesday, March 6, 2019 3:54PM - 4:30PM |
P20.00006: Understanding battery and catalytic reactions via core-level spectroscopies Invited Speaker: Maria Chan Materials often undergo local changes in structure and electronic properties during operations. For example, transition metal oxide battery materials and catalysts often undergo coordination and oxidation state changes. In order to probe these changes, core-level spectroscopy including x-ray absorption, emission, non-resonant and resonant inelastic x-ray scattering, as well as electron energy loss spectroscopy, is often informative. Because of the integrated nature of these signals, the interpretation of these experiments can be at times ambiguous, but can be significantly aided by the use of first principles modeling of core-level spectra. In this talk, we discuss the use of OCEAN [1], a code based on the Bethe-Salpeter Equation, for accurate prediction of core-level spectra, and how the results have helped informed oxygen redox accompanying battery reactions [2,3,4] and detection of CO adsorption during catalytic CO2 reduction reaction [5] in transition metal oxides. |
Wednesday, March 6, 2019 4:30PM - 4:42PM |
P20.00007: Quantum Nonlinear Ferroic Optical Hall Effect Hua Wang, Xiaofeng Qian Nonlinear optical responses provide basis for ultrafast probing of material's intrinsic symmetry [1]. Here we present first-principles theory of quantum nonlinear ferroic optical Hall effect (QNFOHE)[2], a Hall-like photocurrent originated from the second order current response in (multi)ferroics. The interplay of crystalline, permutation, gauge, time reversal symmetries and inherent causality governs the symmetry of QNFOHE. We elucidate QNFOHE in a class of 2D multiferroics [3] using first-principles calculations and group theoretical analysis. Our results suggest QNFOHE-based optical technique as a route for ultrafast characterization of multiferroic orders and domain evolution in multiferroic materials. These microscopic understandings of QNFOHE from first-principles theory, together with very recent discoveries of 2D ferroics/multiferroics, will open up a variety of new avenues for nonlinear optoelectronics. |
Wednesday, March 6, 2019 4:42PM - 4:54PM |
P20.00008: Polar magneto-optical Kerr effect from antiferromagnetic M2As (M=Cr, Mn, and Fe) under external magnetic field Kisung Kang, Krithik Puthalath, David G Cahill, Andre Schleife Polar magneto-optical Kerr effect (PMOKE) is a great tool to detect ferromagnetic domains and their magnetization but is of no use for antiferromagnets without external magnetic field. To understand PMOKE from antiferromagnets under external magnetic field, we use first-principles density functional theory. Due to the lack of net magnetization in the ground state, spin tilting is only induced by an external field, leading symmetry breaking and thus PMOKE signal arises. Based on band structure analysis, exchange splitting and spin-orbit coupling effects are confirmed, similar to ferromagnetic materials. While the spin-orbit coupling is affected little by the external field, exchange splitting arises due to spin tilting. Majority and minority spin states are increasingly separated as external magnetic field increases. Furthermore, in antiferromagnets magnetic susceptibility is related to spin tilting. We compute the magnetic susceptibility of Cr2As, Mn2As, and Fe2As and find that Fe2As presents largest PMOKE signal at a given external magnetic field as well as the largest susceptibility. Large susceptibility leads to larger spin tilting and, hence, more exchange splitting and stronger PMOKE signal. |
Wednesday, March 6, 2019 4:54PM - 5:06PM |
P20.00009: Study of LaScO3 by electronic structure quantum Monte Carlo methods Cody Melton, Lubos Mitas Transition Metal Oxide perovskites (ABO3) are a set of materials that have been widely studied due to the coupling of their charge, spin, orbital, and lattice degrees of freedom, leading to a variety of interesting properties. These materials are typically studied with DFT+U, hybrids, or GW methods to correct for the self-interaction errors within DFT, typically due to the localized nature of the occupied d-orbitals and are often further complicated by various magnetic states. However, even in cases where there is no d-occupancy and the material is a non-magnetic insulator, such as LaScO3, there can be significant errors from these methods due to inaccuracies in the description of electron correlation. For example, the GW methods underestimate the bandgap by roughly 1.5 eV, and hybrid DFT must be tuned in order to reproduce the bandgap. Here, we present a study of LaScO3 using the highly accurate Fixed-Node Diffusion Monte Carlo (FNDMC) method. We show that by carrying out the standard FNDMC methodology, we are able to accurately reproduce the experimental bandgap of LaScO3 without any parameter tuning as is required by DFT and related methods. Additionally, we present calculations of the cohesive energy, equation of state, and other properties using FNDMC. |
Wednesday, March 6, 2019 5:06PM - 5:18PM |
P20.00010: Photoactive metal-organic frameworks for gas separation Roberta Poloni, Claudio Attaccalite, Jing Li, Aseem Rajan Kshiragar Metal-organic frameworks (MOFs) are attracting much attention in recent years for their potential use in CO2 capture technologies. Recently, it has been shown that an efficient capture-and-release process can be obtained upon light treatment in pho- toactive MOFs [1,2]. We demonstrated that in these MOFs the notable change in gas uptake, upon light irradiation, is due to the blocking of the strongly adsorbing metal sites upon isomerization of the azo groups from trans to cis [3]. Interestingly, our study suggests a large fraction of cis at the photostationary state. A large S1/S2 absorption band separation between trans and cis within the MOF could support this hypothesis. In order to address this, we have computed the optical absorption spectra of these MOFs and their ligands using embedded GW/BSE calculations as implemented in FIESTA. Embedding is considered first at the DFT level (COSMO solvation model and ESP charges) and then, in the calculation of the modified screened Coulomb potential. CASSCF/CASPT2 and periodic GW/BSE are performed to benchmark, respectively, the DFT starting point and the choice of the fragment. Work supported by ANR-15-CE06-0003-01. [1] Park et al, JACS 134, 99 (2012); [2] Wang et al, Nature Commun. 7, 13872 (2016); |
Wednesday, March 6, 2019 5:18PM - 5:30PM |
P20.00011: Electronic and Magnetic Propoerties of KTa1−xMnxO 3 ; (x = 0, 0.50, 0.67) Gopi Chandra Kaphle, Nirmala Adhikari KTa1−xMnxO3 (x = 0, 0.50, 0.67) are perovskites used for fuel cells, memories devices, and spintronic applications. In the present work, we performed the first-principles calculations to study the structural, electronic and magnetic properties of pristine KTaO3 perovskite and Manganese doped perovskites KTa1−xMnxO3 system along Ta site of super-cell. Our study based on super-cell calculations. Our finding shows that the pure perovskite KTaO3 is indirect type band gap semiconductor having band gap 2.13 eV which is close agreement with experimental reported value 2.15 eV within 1% deviation. In the study of Mn doped system, we observed that there is indirect band gap decrease from 2.13 eV to 0.84 eV at 50% Mn doped on perovskite KTa0.5Mn0.5O3 along Ta site and 0.81eV at 67% Mn doped on perovskite KTa0.33Mn0.67O3 along Ta site. Further investigations shows antisymmetric distribution of DOS for spin-up and spin-down electronic states for Mn doped states. The contribution to total DOS is due to 2p-orbital of oxygen and 3d-orbital of manganese around the Fermi level. Whole doped system behaves as half metallic. |
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