Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session E7: First-Principles Modeling of Excited-State Phenomena I: Methodological AdvancesFocus
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Sponsoring Units: DCOMP DCP DMP Chair: Volker Blum, Duke University Room: 266 |
Tuesday, March 14, 2017 8:00AM - 8:12AM |
E7.00001: Koopmans-compliant functionals as spectral theories: molecules, solids, and liquids Nicola Marzari, Ngoc Linh Nguyen, Nicola Colonna, Andrea Ferretti Koopmans-compliant functionals\footnote{I. Dabo, M. Cococcioni, and N. Marzari, arXiv:0901.2637 (2009); I. Dabo {\it et al.}~Phys.~Rev.~B 82 115121 (2010).} enforce a generalized criterion of piecewise linearity with respect to the fractional removal or addition of an electron (i.e. a charged excitation) from any orbital in local or semi-local total-energy DFT functionals. By doing so they lead to beyond-DFT orbital-density dependent functionals that are able to deliver spectroscopic properties. We'll present an overview of the current status when applied to ionization potentials, electron affinities, photoemission spectra, and band gaps of molecules, solids, and liquids, with results that are comparable or slightly superior to many-body perturbation theory, but with functionals that rely only on the physics of the PBE generalized-gradient approximation. [Preview Abstract] |
Tuesday, March 14, 2017 8:12AM - 8:24AM |
E7.00002: Screening and linear response in Koopmans-compliant functionals Nicola Colonna, Ngoc Linh Nguyen, Andrea Ferretti, Nicola Marzari The need to describe relaxation effects in the fractional removal or addition of an electron requires screening the orbital-dependent corrections of Koopmans-compliant functionals. Here, we present a general method to incorporate orbital-by-orbital screening based on linear-response theory. We illustrate the importance of such generalization when dealing with challenging system containing orbitals with very different chemical character, such as transition-metal complexes. Results for ionization potentials, when compared with many-body perturbation theory (MBPT) and experiments, show a remarkably good performance, comparable to the most accurate MBPT approach (G0W0@PBE0). [Preview Abstract] |
Tuesday, March 14, 2017 8:24AM - 8:36AM |
E7.00003: Ultrafast phase transitions in advanced materials: review of some experiments and a new theoretical approach Roland Allen, Ayman Abdullah-Smoot, Michelle Gohlke, David Lujan, James Sharp, Ross Tagaras This talk will review some experimental studies of advanced materials responding to fast intense laser pulses, including light-induced superconductivity in cuprates [1]. A new method will be introduced for treating ultrafast phase transitions, such as those involving superconductivity, magnetism, charge density waves, and spin density waves. This method is made possible by the fact that the density-functional-based technique emphasized here (and also standard density-functional approaches and other first-principles techniques, as long as they include nuclear motion) can yield a true electronic temperature [2]. Illustrative results will be presented for a simple model, with the electronic temperature immediately after the laser pulse calculated as a function of the fluence. \\ 1. D. Fausti, R. I. Tobey, N. Dean, S. Kaiser, A. Dienst, M. C. Hoffmann, S. Pyon, T. Takayama, H. Takagi, and A. Cavalleri, “Light-Induced Superconductivity in a Stripe-Ordered Cuprate”, Science 331, 189 (2011). \\ 2. Zhibin Lin and Roland E. Allen, “Ultrafast equilibration of excited electrons in dynamical simulations”,J. Phys. Condens. Matter 21, 485503 (2009). [Preview Abstract] |
Tuesday, March 14, 2017 8:36AM - 8:48AM |
E7.00004: A non-adiabatic exchange-correlation potential for strongly-correlated materials: local impurity approximation and beyond Volodymyr Turkowski, Shree Ram Acharya, Talat S. Rahman We formulate a non-adiabatic Time-Dependent Density-Functional Theory (TDDFT) for materials with strong local (on-site) electron-electron interactions. In this approach, the TDDFT exchange-correlation (XC) potential is derived from the expression for the single electron local-in-space self-energy obtained from the many-body Dynamical Mean-Field Theory (DMFT) solution for an effective Hubbard model (Sham-Schluter equation). We attest to the validity of the formalism through good agreement of our TDDFT results with the nonequilibrium DMFT solution for the ultrafast excited state charge dynamics of the Hubbard model for a system perturbed by a short laser pulse. To include the effects of spatial nonlocality in the XC potential, we propose a generalization of the formalism by including a momentum-dependent correction to the DMFT electron self-energy (the dynamical vertex approximation). We apply the approach to analyze the ultrafast breakdown of the insulating phase in VO2 and show that the TDDFT results are also in a good agreement with available experimental data. The developed approach can be used to study the ultrafast response of complex strongly correlated materials, a task that current many-body approaches fail to address fully because of their inherent computational demands. [Preview Abstract] |
Tuesday, March 14, 2017 8:48AM - 9:00AM |
E7.00005: Quasiparticle spectra obtained through stochastic many-body methods Vojtech Vlcek, Roi Baer, Eran Rabani, Daniel Neuhauser We present the linearly scaling stochastic approach to many-body perturbation theory and to calculations of quasiparticle energies in $G_0W_0$ approximation and beyond. Our approach overcomes the steep scaling of conventional deterministic schemes. Further, it allows a simple incorporation of higher order interactions (vertex corrections). Exemplifying on covalently bonded systems (nanocrystals and polymer chains), we show practical calculations of quasiparticle spectra, and self-energies for large systems with thousands of electrons. The linear scaling is fundamental nature of our approach, which does not rely on a particular character of the electronic structure (e.g., there is no need for sparsity of the density matrices). The scaling prefactor is small so the stochastic $G_0W_0$ method is thus a method of choice for all systems from few tens to thousands -- and in the near horizon hundreds of thousands -- of electrons. [Preview Abstract] |
Tuesday, March 14, 2017 9:00AM - 9:12AM |
E7.00006: Temperature dependence of the one-electron Green's function within the cumulant formalism J. J. Kas, J. J. Rehr Recently there has been renewed interest in the cumulant expansion for the one-electron Green's function due to its success in explaining inelastic losses and many-body effects beyond the GW approximation in x-ray photoemission and absorption spectra. For example, the approach has shown great promise in reproducing the observed multiple-plasmon satellites in the XPS of metals and semi-conductors,\footnote{J. Zhou et al., J. Chem. Phys. 143, 184109 (2015).} as well as the satellite structure in charge-transfer systems such as CeO2.\footnote{J.J. Kas, J.J. Rehr and J.B. Curtis, Phys. Rev. B 94, 035156 (2016).} Here we investigate the role of temperature on these satellite features using a finite temperature cumulant expansion for the retarded one-electron Green's function. The cumulant is related to the retarded GW self-energy, which is determined from the Matsubara Green's function and response function within the RPA. We apply the method to the uniform electron gas over a wide range of temperatures, and we discuss the implications of these results on measurements of XPS and Compton scattering, which can be used as a thermometer for warm dense matter. [Preview Abstract] |
Tuesday, March 14, 2017 9:12AM - 9:24AM |
E7.00007: A Many-Body Formalism of $\Delta$SCF Approach for Simulating X-Ray Spectra from First-Principles YUFENG LIANG, John Vinson, Sri Pemmaraju, Walter Drisdell, Eric Shirley, David Prendegast Accurately reproducing X-ray spectral fingerprints for materials characterization relies heavily on how to correctly model the many-electron response to the generation of an X-ray core hole. In this talk, we present a novel first-principles theory for simulating X-ray spectra that is based on many-electron wavefunctions. The proposed theory go beyond the electron-hole correlations within the Bethe-Saltpeter Equation and consider higher-order vertex corrections up to the level of Mahan-Nozi\'eres-De Dominicis (MND) theory. An efficient algorithm is invented to incorporate these many-electron processes by using linear algebra rather than iterating over all Feynman diag [Preview Abstract] |
Tuesday, March 14, 2017 9:24AM - 9:36AM |
E7.00008: The Hubbard dimer: exact dynamic exchange-correlation kernel, single and double excitations of a strongly correlated problem Jaime Ferrer, Diego Carrascal, Neepa Maitra, Kieron Burke The Hubbard dimer is an exactly solvable model of a strongly correlated problem [1]. We develop here its exact frequency-dependent exchange-correlation kernel. Armed with this, we analyse the behaviour of the single and double excitations of the model as they evolve from the weak correlation regime deep into the strongly-correlated Mott-Hubbard regime. [1] D. J. Carrascal, J. Ferrer, J. C. Smith and K. Burke, The Hubbard dimer: a density functional case study of a many-body problem, Journal of Physics: Condensed Matter 27, 393001 (2015). [Preview Abstract] |
Tuesday, March 14, 2017 9:36AM - 9:48AM |
E7.00009: Linked-cluster formulation of screened electron-hole interaction from explicitly-correlated geminal functions without using unoccupied states Arindam Chakraborty, Michael Bayne The accurate determination of the electron-hole interaction kernel remains a significant challenge for precise calculations of optical properties in the GW+BSE formalism. The inclusion of unoccupied states has long been recognized as the leading computational bottleneck that limits the application of this approach for large finite systems. In this work, we present an alternative derivation that avoids using unoccupied states to construct the electron-hole interaction kernel. The central idea of our approach is to use explicitly correlated geminal functions for treating electron-electron correlation for both ground and excited state wave functions. We demonstrate with diagrammatic techniques that the frequency-dependent electron-hole kernel can be expressed in terms of connected closed-loop diagrams. We show that the cancelation of disconnected diagrams is a consequence of the linked-cluster theorem in real-space representation and the resulting renormalized operators are equivalent to infinite-order summations of particle-hole diagrams. The derived electron-hole interaction kernel was used to calculate excitation energies in atoms, molecules, clusters and quantum dots and the results for these systems were compared with CIS, TDHF, TDDFT, EOM-CCSD, and GW+BSE calculations. [Preview Abstract] |
Tuesday, March 14, 2017 9:48AM - 10:24AM |
E7.00010: Connecting Interface Structure to Energy Level Alignment at Aqueous Semiconductor Interfaces Invited Speaker: Mark Hybertsen Understanding structure-function relationships at aqueous semiconductor interfaces presents fundamental challenges, including the discovery of the key interface structure motifs themselves. Important examples include the alignment of electrochemical redox levels with the semiconductor band edges and the identification of catalytic active sites. We have developed a multistep approach, initially demonstrated for GaN, ZnO and their alloys, motivated by measured high efficiency for photocatalytic water oxidation. The interface structure is simulated using ab initio molecular dynamics (AIMD).\footnote{N. Kharche, et al., \textit{Phys. Chem. Chem. Phys.} 16, 12057 (2014)} The calculated, average interface dipole is combined with the GW approach from many-body perturbation theory to calculate the energy level alignment between the semiconductor band edges and the centroid of the occupied 1b1 energy level of water and thus, the electrochemical levels.\footnote{N. Kharche, et al., \textit{Phys. Rev. Lett.} 113, 176802 (2014)} Cluster models are used to study reaction pathways.\footnote{M. Z. Ertem, et al., \textit{ACS Catal.} 5, 2317 (2015)} The emergent interface motif is the full (GaN) or partial (ZnO) dissociated interface water layer. \newline \newline Here I will focus on the aqueous interfaces to the stable TiO$_{\mathrm{2}}$ anatase (101) and rutile (110) facets. The AIMD calculations reveal interface water dissociation and reassociation processes through distinct pathways: one direct at the interface and the other via a spectator water molecule from the hydration layer. Comparisons between the two interfaces shows that the energy landscape for these pathways depends on the local hydrogen bonding patterns and the interplay with the interface template. Combined results from different initial conditions and AIMD temperatures demonstrate a partially dissociated interface water layer in both cases. Specifically for rutile, structure and the GW-based analysis of the interface energy level alignment agree with experiment. Finally, hole localization at different interface structure motifs will be discussed. \newline \newline Work performed in collaboration with J. Lyons, N. Kharche, M. Ertem and J. Muckerman, done in part at the CFN, which is a U.S. DOE Office of Science Facility, at BNL under Contract No. DE-SC0012704 and with resources from NERSC under Contract No. DE-AC02-05CH11231. [Preview Abstract] |
Tuesday, March 14, 2017 10:24AM - 10:36AM |
E7.00011: Reduced order polarizability method for large scale GW calculations Minjung Kim, Subhasish Mandal, Eric Mikida, Kavitha Chandrasekar, Eric Bohm, Nikhil Jain, Laxmikant Kale, Glenn Martyna, Sohrab Ismail-Beigi The GW method is an important tool for accurate calculation, from first principles, of excited electronic systems. However, the GW method has not been routinely applied to large scale materials physics or chemistry problems due to its heavy computational load and large memory requirements. The most computationally intense part of GW calculation is the calculation of the polarizability matrix: for standard ``sum-over-states'' approaches, it scales as N$^4$ where N is the number of electrons in the system. As part of our team's effort towards developing massively parallel GW software that can be readily applied to large-scale systems, we have implemented a real-space algorithm which greatly reduces the number of fast Fourier-transform to build polarizability matrix (in a plane wave basis). Using this real-space representation of the polarizability matrix, we are then able to develop two types of cubic-scaling polarizability methods that use interpolation or Gaussian quadrature to simplify the treatment of energy dependencies. We will describe the methods and their accuracies and efficiencies when applied to crystalline materials. [Preview Abstract] |
Tuesday, March 14, 2017 10:36AM - 10:48AM |
E7.00012: Constructing the GW self-energy of a point defect from the perfect crystal and the near neighborhood of the defect Dmitry Skachkov, Mark van Schilfgaarde, Walter Lambrecht The full-potential linearized muffin-tin orbital method allows for a real space representation of the GW or quasi-particle self-consistent (\textit{QS})GW self-energy $\Sigma_{\mathrm{R,L;R\mbox{'}+T,L\mbox{'}}}$. This can be used to construct the self-energy matrix for a point defect system in a large supercell from that of the perfect crystal in the primitive cell and the self-energy of the defect site and its near neighborhood, obtained self-consistently in a smaller supercell. At the interface between both regions we can average the two types of $\Sigma _{\mathrm{R,L;R\mbox{'}+T,L\mbox{'}}}$ matrix blocks. The result relies on the limited range of the self-energy matrix in real space. It means that we can calculate the quasiparticle energy levels of the defect system at essentially the cost of a DFT calculation and a few \textit{QS}GW calculations for relatively small systems. The approach presently focuses on quasiparticle energy levels of band structures of the defect system rather than total energies. We will present test results for As$_{\mathrm{Ga\thinspace }}$in GaAs, Zn$_{\mathrm{Ge}}$ in ZnGeN$_{\mathrm{2}}$, N$_{\mathrm{O}}$, V$_{\mathrm{O}}$, V$_{\mathrm{Zn}}$, and N$_{\mathrm{O}}-$V$_{\mathrm{Zn}}$ in ZnO. [Preview Abstract] |
Tuesday, March 14, 2017 10:48AM - 11:00AM |
E7.00013: Spin-wave excitations and electron-magnon scattering from many-body perturbation theory Christoph Friedrich, Mathias C. T. D. M\"uller, Stefan Bl\"ugel We study the spin excitations and the electron-magnon scattering in bulk Fe, Co, and Ni within the framework of many-body perturbation theory as implemented in the full-potential linearized augmented-plane-wave method. Starting from the \textit{GW} approximation we obtain a Bethe-Salpeter equation for the magnetic susceptibility treating single-particle Stoner excitations and magnons on the same footing. Due to approximations used in the numerical scheme, the acoustic magnon dispersion exhibits a small but finite gap at $\Gamma$. We analyze this violation of the Goldstone theorem and present an approach that implements the magnetic susceptibility using a renormalized Green function instead of the non-interacting one, leading to a substantial improvement of the Goldstone-mode condition [1]. Finally, we employ the solution of the Bethe-Salpeter equation to construct a self-energy that describes the scattering of electrons and magnons. The resulting renormalized band structures exhibit strong lifetime effects close to the Fermi energy. We also see kinks in the electronic bands, which we attribute to electron scattering with spatially extended spin waves. \\ {}[1] M\"uller et al., Phys. Rev. B \textbf{94}, 064433 (2016). [Preview Abstract] |
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