Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L43: Firstprinciples modeling of excitedstate phenomena in materials VII: Electronic excitations: DFT and BeyondFocus

Hide Abstracts 
Sponsoring Units: DCOMP DMP DCP Chair: Michiel van Setten, IMEC Room: 702 
Wednesday, March 4, 2020 8:00AM  8:36AM 
L43.00001: Transition to metallization in warm dense heliumhydrogen mixtures using stochastic density functional theory Invited Speaker: Eran Rabani The KuboGreenwood (KG) formula is often used in conjunction with KohnSham (KS) density functional theory (DFT) to compute the optical conductivity, particularly for warm dense matter. For applying the KG formula, all KS eigenstates and eigenvalues up to an energy cutoff are required and thus the approach becomes computationally expensive, especially for high temperatures and large systems, scaling cubically with both system size and temperature. 
Wednesday, March 4, 2020 8:36AM  8:48AM 
L43.00002: Towards a systematic multiscale method for excitations in molecular materials in the BigDFT code Martina Stella, Laura E Ratcliff, Luigi Genovese Understanding excitations is critical in spectroscopy as well as in technological applications, e.g. identifying where excited states lay for molecules in crystals is crucial for guiding experimentalists in locating excitation sources. Another example is thermally activated delayed fluorescence (TADF), a mechanism for designing the next generation of OLEDs (Organic Light Emitting Diodes materials) that are less environmentally harmful than the previous generation. Excitations in TADF materials exhibit an intricate mixture of chargetransfer and local nature and can be strongly influenced by the host material. Modelling TADF (e.g identifying the best performing material) or locating excited states, thus, requires an accurate methodology that explicitly includes environmental effects. We are developing a multiscale approach in the BigDFT code where high accuracy is combined with the ability of treating big systems to eventually go beyond implicit models. BigDFT runs on parallel architectures and can treat large systems with high, controllable precision. As a first step towards a robust methodology, we assess the performance of a promising new constrainedDFT approach recently developed in our group for various classes of excitations in comparison to standard methods (TDDFT). 
Wednesday, March 4, 2020 8:48AM  9:00AM 
L43.00003: MuST: An integrated ab initio framework for the study of disordered structures Yang Wang, Markus Eisenbach, Xianglin Liu, Khorgolkhuu Odbadrakh, Hanna Terletska, KaMing Tam, Yi Zhang, liviu chioncel The effect of disorder in materials is of great fundamental and technological interest. In this presentation, I will introduce a new public software package, called MuST, designed for enabling first principles investigation of disordered materials. MuST is developed based on fullpotential multiple scattering theory with Green function approach, and is built upon decades of development of research codes that include KorringaKohnRostoker Coherent Potential Approximation (KKRCPA), a highly efficient ab initio method for the study of random alloys, and Locally Selfconsistent Multiple Scattering (LSMS) method, a linear scaling ab initio code capable of treating extremely large disordered systems from the first principles using the largest parallel supercomputers available. Strong disorder and localization effects can also be studied in real system within the LSMS formalism with cluster embedding in an effective medium with the Typical Medium Dynamical Cluster Approximation (TMDCA), which enables a scalable approach for first principles studies of quantum materials. 
Wednesday, March 4, 2020 9:00AM  9:12AM 
L43.00004: Understanding the chemical enhancement mechanism of 2D substrate enhanced Raman Spectroscopy (2DSERS). Kanchan Ulman, Su Ying Quek Surfaceenhanced Raman spectroscopy (SERS) is a well established field which utilizes the enhancement of Raman signals for molecules on metal substrates, resulting in applications of this phenomena for detection and identification of trace concentrations of molecules. In recent years, twodimensional (2D) materials like graphene, hBN and MoS_{2} are being used as substrates for SERS, giving rise to rapidly growing field of 2Dsubstrate enhanced Raman spectroscopy (2DSERS). In conventional SERS, the enhancement factor is dominated by an electromagnetic enhancement mechanism, as compared to the smaller chemical enhancement effect. In 2DSERS however, this chemical enhancement effect (which stems from electronphonon coupling within the molecule and substrate) is thought to play a dominating role. Yet, the detailed understanding of the chemical enhancement effect in 2DSERS is still lacking. Using first principles calculations, we study the chemical enhancement mechanism using typical probe molecules such as pyridine and pthalocyanine on 2D substrates, highlighting the role of electronphonon coupling and chargetransfer excitons in the chemical enhancement mechanism of 2DSERS. 
Wednesday, March 4, 2020 9:12AM  9:24AM 
L43.00005: Local mixing in modified BeckeJohnson potential for lowdimensional systems Tomas Rauch, Miguel Marques, Silvana Botti We propose an extension to the modified BeckeJohnson potential [1] that enables its use to study both heterogeneous and lowdimensional systems. This is achieved by using a coordinatedependent expression for the c parameter, in contrast to the original global formulation. Our functional builds on the excellent description of bulk band gaps of the modified BeckeJohnson potential and preserves its modest computational effort. Furthermore, it yields with one single calculation banddiagrams and bandoffsets of heterostructures, interfaces, and surfaces. We exemplify the usefulness and efficiency of our local functional by testing it for a series of semiconductor interfaces, surfaces, twodimensional systems, and molecules. 
Wednesday, March 4, 2020 9:24AM  9:36AM 
L43.00006: Periodic Electronic Structure Calculations With Density Matrix Embedding Theory Hung Q Pham, Matthew R Hermes, Laura Gagliardi We developed a periodic version of density matrix embedding theory, DMET, with which it is possible to perform electronic structure calculations on periodic systems, and compute the band structure of solidstate materials. Electron correlation can be captured by means of a local impurity model using various wave function methods, like, for example, full configuration interaction, coupled cluster and multiconfigura tional methods. The method is able to describe not only the groundstate energy but also the quasiparticle band picture via the realmomentum space implementation. We investigate the performance of periodic DMET in describing the groundstate energy as well as the electronic band structure for onedimensional solids. Our results show that DMET is in good agreement with other manybody techniques at a cheaper com putational cost. We anticipate that periodic DMET can be a promising first principle method for strongly correlated materials. 
Wednesday, March 4, 2020 9:36AM  9:48AM 
L43.00007: Density Functional Theorybased study of charge transfer in doped silicon nanowire with gold leads: A toy model for the pn junction photovoltaic device Nathan Walker, Dmitri Kilin, Andrei Kryjevski We analyze a toy model for pn junction photovoltaic devices by simulating photoexcited state dynamics in silicon nanowires doped with aluminum and phosphorus atoms and capped with gold leads. We use Boltzmann transport equation (BE) that includes phonon emission, carrier multiplication (CM), and exciton transfer. BE rates are computed using nonequilibrium finitetemperature manybody perturbation theory (MBPT) based on Density Functional Theory simulations, including excitonic effects from BetheSalpeter Equation (see A. Kryjevski, D. Mihaylov, and D. Kilin, J. of Phys. Chem. Lett., 9(19) (2018), A. Kryjevski, D.Mihaylov, S. Kilina, and D. Kilin, J. of Chem. Phys., 147, 154106 (2017)). We compute total charge transfer amount generated from the initial photoexcitation and find an enhancement when CM is included. 
Wednesday, March 4, 2020 9:48AM  10:00AM 
L43.00008: HJAggregate Theory Applied to Interacting SP^{3}Hybridization Defects in Carbon Nanotubes Braden Weight, Andrew E Sifain, Brendan J Gifford, Svetlana Kilina, Sergei Tretiak Singlewalled carbon nanotubes (CNTs) have been recently studied in greater depth due to their promise of superior electronic properties for tunable emission of infrared energies. Optical features of functionalized CNTs (via SP^{3}hybridization defects) have been narrowed to only a few main parameters: (I) chirality, (II) defect configuration, and (III) defect electronegativity. Previous theoretical studies have been directed at single defects (comprised of a pair of functional groups) attached to the CNT surface, and, until recently, no literature has discussed the effects of defect concentration on CNTs in any depth [1,2]. In this work, we aim to model the interactions between nearby defects using density functional theory (DFT) and, extending to excited states, timedependent DFT (TDDFT) in order to fit these interactions to a wellknown descriptor of analogous systems known as HJaggregate theory. 
Wednesday, March 4, 2020 10:00AM  10:12AM 
L43.00009: Identifying sources of error in finite temperature calculations for molecules and solids using density matrix quantum Monte Carlo Hayley Petras, Sai Ramadugu, James Shepherd Density matrix quantum Monte Carlo (DMQMC) calculates exactonaverage finite temperature electronic energies in a finite basis. This method has shown promise when applied to model systems like the electron gas (Phys. Rev. Lett. 117, 115701) but it is not well understood whether these findings are transferrable to real systems and to what extent strong correlation can affect our ability to run calculations on a system. Calculations on small molecules and solids (in a periodic basis set) will be presented including a resolution to previous convergence issues for the H_{10} chain. Finally, the computational cost scaling of DMQMC will be identified. 
Wednesday, March 4, 2020 10:12AM  10:24AM 
L43.00010: Dynamical configuration interaction study of free base porphyrin Marc Dvorak, Patrick Rinke We apply the recently developed dynamical configuration interaction (DCI) theory to study the lowlying excited states of free base porphyrin. In DCI [1,2], we diagonalize the exact manybody Hamiltonian in the stronglycorrelated active space with the wave function technique of configuration interaction (CI). Additionally, the effects of the surrounding degrees of freedom are downfolded onto an energydependent correction added to the bare CI Hamiltonian. These corrections are approximated with manybody Green's function theory in the GW approximation. Freebase porphyrin is the largest system studied with DCI so far and serves as an important test of the numerical implementation, scalability, and size consistency of the theory. Our DCI results for excitation energies of porphyrin are in good agreement with past work. 
Wednesday, March 4, 2020 10:24AM  10:36AM 
L43.00011: Light driven NonThermal Amorphization Mechanism of Phase Change Material Subodh Tiwari, Aiichiro Nakano, Fuyuki Shimojo, Rajiv Kalia, Paulo Branicio, Priya Vashishta Phasechange materials (PCM) are exploited in modern electronics due to the extreme electrooptical contrast between crystalline and amorphous states. However, atomistic mechanisms governing photoexcitationinduced athermal amorphization processes are still unknown. We perform excitedstate dynamics within the framework of density functional theory to understand the mechanism behind such crystallinetoamorphous transition for Germanium Telluride (GeTe). Amorphous phase induced due to excitedstate dynamics was characterized by computing diffraction pattern. Further analysis of bondoverlap population shows charge transfer of electron from GeTe bonding orbitals to GeGe antibonding orbitals. Such charge transfer process leads to the destabilization of GeTe crystals, eventually leading to amorphization. Rapid heat extraction during excitedstate simulation does not lead to amorphous phase. Since structural transformation limits the lifetime of PCMbased devices, a complete understanding behind mechanism may allow us to a new avenue to design better devices. 
Wednesday, March 4, 2020 10:36AM  10:48AM 
L43.00012: First Principles Simulations of Hg_{x}Cd_{1x}(S,Se) Optical Properties Erick Hernandez Alvarez, Andrew Michael Smith, Andre Schleife Mercury cadmium chalcogenide alloy quantum dots (QDs) are a promising material to meet the rapidly growing need for materials with emission in the biological nearinfrared (NIR) window (7002,000 nm) where tissue transparency is high and autofluorescence noise is low. Cation exchangemediated alloying is an effective way to tune the QD emission wavelength continuously across the entire visible and NIR spectra without altering the QD’s physical dimensions. Here we describe the optical properties of zinc blende Hg_{x}Cd_{1x}S and Hg_{x}Cd_{1x}Se alloys from first principles simulations across the compositional space. We use density functional theory to compute electronic band structures of the binary mercury and cadmium chalcogenide systems and their intermediate ternary alloys. We then compute the corresponding optical spectra and describe the extent of the effect of spinorbit coupling on the calculated photophysical properties. Comparison to measured absorption spectra of mercury cadmium chalcogenide alloy QDs provides insights into how photophysical parameters can be achieved with specific compositions and nanocrystal sizes. 
Wednesday, March 4, 2020 10:48AM  11:00AM 
L43.00013: DFT: the lore of smoothing and tetrahedra is wrong Jeremy Jorgensen, Gus Hart Smoothing and tetrahedron methods in density functional theory (DFT) codes were developed to improve the robustness and efficiency of DFT codes. Tests we have performed demonstrate that both methods fail to accomplish either assertion. We have run ~20,000 DFT calculations in VASP and Quantum Espresso with various types and amounts of smoothing on 12 metals. The rate of convergence of the total energy for calculations with smoothing is often worse than those without smoothing, and smoothing does not result in a reduction in the number of selfconsistency cycles when compared to runs without smoothing. We obtained similar results in comparisons involving tetrahedron methods. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2022 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700