Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E20: First-principles Modeling of Excited-state Phenomena in Materials IV: Time-dependent Density Functional TheoryFocus
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Sponsoring Units: DCOMP DMP Chair: Sahar Sharifzadeh, Boston University Room: BCEC 157A |
Tuesday, March 5, 2019 8:00AM - 8:36AM |
E20.00001: Time-dependent density-functional approaches for excitons: the pros and cons of long-range corrected exchange-correlation kernels Invited Speaker: Carsten Ullrich Time-dependent density-functional theory (TDDFT) is, in principle, more efficient than the Bethe-Salpeter equation for calculating the optical properties of semiconductors and insulators. However, finding accurate exchange-correlation (xc) kernels for describing excitons is quite challenging: standard local and semilocal approximations lack the proper long-range behavior and do not produce bound excitons. This talk presents a systematic assessment of a class of long-range corrected (LRC) xc kernels which have shown promise for excitonic effects. It is found that no existing LRC kernel is capable of simultaneously producing good optical spectra and quantitatively accurate exciton binding energies for both semiconductors and insulators. We discuss strategies to improve the TDDFT treatment of excitons via semiempirical LRC xc kernels and screened hybrid approaches. |
Tuesday, March 5, 2019 8:36AM - 8:48AM |
E20.00002: Exact exchange-correlation kernels for optical spectra Mike Entwistle, Rex W Godby Time-dependent density-functional theory (TDDFT) is in principle a powerful technique for simulating the time-evolution of systems of interacting electrons. Whilst TDDFT has had notable successes, the usual adiabatic functionals within the linear response regime can fail badly when applied to problems such as optical absorption spectra. By reverse-engineering numerically exact calculations of the ground and excited many-body states, and response functions, of prototype one-dimensional systems, we obtain the exact exchange-correlation kernel fxc(x,x',ω) for each system. We explore the properties of these exact xc kernels, and suggest how common approximations may be improved. |
Tuesday, March 5, 2019 8:48AM - 9:00AM |
E20.00003: Accelerating excited-state calculations in NanoGW using an interpolative separable density fitting method Weiwei Gao, James Chelikowsky The NanoGW package implements some of the most widely used methods for calculating excited-state properties, including time-dependent density function theory (TDDFT), GW approximation, and Bethe-Salpeter equation in the single-particle orbital basis. Solving Casida’s equation of TDDFT and performing GW/BSE calculations with NanoGW involve the computation of many electron-repulsion integrals. We will discuss the implementation of the interpolative separable density fitting (ISDF) method, a new density-fitting method [1] with O(Natom3) computational complexity, in NanoGW. With ISDF method, we can reduce the number of electron-repulsion integrals from O(Natom4) to O(Natom2). |
Tuesday, March 5, 2019 9:00AM - 9:12AM |
E20.00004: Floquet theory for the electronic stopping of projectiles in solids Nicolo' Forcellini, Emilio Artacho The problem of electronic stopping is traditionally approached and understood in the context of linear response theory[1], or a full non-linear theory for jellium[2]. First-principles quantitative simulations using time dependent density functional theory show reasonably predictive accuracy but remain computationally expensive and do not provide a clear, intuitive understanding of the stopping processes. |
Tuesday, March 5, 2019 9:12AM - 9:24AM |
E20.00005: Electronic stopping of protons in anisotropic weakly bound materials Jessica F. K. Halliday, Pere Alemany, Emilio Artacho Ions shooting through condensed matter dissipate their kinetic energy by transferring it to the target's electrons and nuclei. At high velocities (above 1% of the spped of light) the stopping is mostly electronic, in a highly non-equilibrium, non-adiabatic process. First-principles simulations of such processes have been quite successfully performed in the last decade for varied systems. Here we present results for electronic stopping power for protons in graphite and ideal crystalline polyethylene, anisotropic systems with strong bonding in two dimensions and weakly bound in the other dimension, and vice-versa, respectively. They are based on time-dependent density-functional theory in real time, and using a basis of atomic orbitals (LCAO) within the SIESTA program. Results of the effect of trajectory orientation and impact parameter will be presented, displaying a transition from electronic-structure dependence at low velocity, to a regime at higher velocities in which the particle density along the projectile's path dominates. A reformulation of the TD-LCAO formalism and its implications for numerical simulations will be also presented. |
Tuesday, March 5, 2019 9:24AM - 9:36AM |
E20.00006: Electronic excitations in proton-irradiated ice via Real-Time TDDFT Daniel Muñoz-Santiburcio, Emilio Artacho Describing the interaction of water ice with highly energetic particles at the atomistic/electronic scale is of great importance to understand many astrophysical/chemical processes taking place in interstellar dust, comets, asteroids and satellites exposed to such particles present in solar wind, cosmic rays or strong magnetospheres. |
Tuesday, March 5, 2019 9:36AM - 9:48AM |
E20.00007: Electronic stopping power from time-dependent density-functional theory in Gaussian basis Ivan Maliyov, Fabien Bruneval, Jean-Paul Crocombette Irradiation damage in condensed matter has been identified as central to nuclear materials, electronics, nuclear medicine. The interaction between an irradiating ion and a target material is measured by the stopping power, defined as the energy transfer from the projectile to the material per penetration distance. The most important ionic energy loss channel occurs through electronic excitations. This work is devoted to the ab initio calculations of the electronic stopping power. |
Tuesday, March 5, 2019 9:48AM - 10:00AM |
E20.00008: Charge equilibration and electronic stopping for self-irradiated silicon Cheng-Wei Lee, Andre Schleife Charged energetic particle radiation has technological interest in applications including nuclear energy, outer space, medicine, and fundamental research. As a result of irradiation, damage, including point defects, forms and ultimately determines the material properties. Therefore, understanding the underlying interactions between charged particles and a material from first principles is important. Recently, we investigated heavy (silicon) projectiles traversing crystalline bulk silicon and found a pronounced dependence of electronic stopping on the initial projectile charge state. This effect was not observed for light projectiles impacting metal or semiconductor targets. To understand this, we analyze the dynamics of charge equilibration, influence of the impact parameter, and contributions of core and valence electrons to electronic stopping. We observe that the equilibrium charge state of the Si projectile depends on the impact parameter and ultimately dominates electronic stopping. We also predict that this effect should be observable experimentally for large-Z projectiles of different charge, on hyper-channeling trajectories, e.g. in a thin film. |
Tuesday, March 5, 2019 10:00AM - 10:12AM |
E20.00009: Vicinage effects in the stopping power of molecular hydrogen in aluminum Edwin Quashie, Xavier Andrade, Alfredo A. Correa Using time-dependent density functional theory (TDDFT) we calculate the electronic stopping power of the hydrogen molecule, H2, projectile in aluminum over a wide range of velocities where we take into account the effect of the drag dynamics of excited electrons. The electronic excitations determine the stopping power and also a change the interatomic forces of the molecule during the trajectories. |
Tuesday, March 5, 2019 10:12AM - 10:24AM |
E20.00010: Negative Differential Conductivity in Semiconductors from First Principles Rafi Ullah, Xavier Andrade, Alfredo A. Correa The negative differential conductivity (NDC) in gas-discharge tubes had been known long before [1] it was discovered in solids [2]. It was the discovery of NDC in semiconductors that invoked renewed interest in this area and opened it to applications in electronics [3]. Recently NDC has been observed in a quantum gas of neutral atoms [4]. It has been observed and predicted in different physical systems, including in normal metals [5], but the underlying physics is very different in each of those systems. In semiconductors it is mainly attributed to the electron transfer between different energy sub-bands. The transport phenomena in general and the NDC in semiconductors in particular is non-linear in |
Tuesday, March 5, 2019 10:24AM - 10:36AM |
E20.00011: Exchange and correlation effects in finite-temperature TDDFT John Rehr, Joshua Kas We discuss the finite-temperature (FT) generalization of time-dependent density functional theory (TDDFT) [1]. Formally the theory is analogous to that at temperature T = 0. In the local density approximation, the FT exchange-correlation kernel fxc(T,n) can again be expressed as a density derivative of the exchange correlation potential d vxc(T,n)/dn, where n = N/V is the electron number density. An approximation for the TDDFT kernel fxc(T,n) is obtained from the FT generalization of the retarded cumulant expansion applied to the homogeneous electron gas [2]. Results for fxc and for the FT loss function are shown for a wide range of temperatures and densities, including the warm dense matter regime with temperatures of order TF , the electron degeneracy temperature. The FT cumulant Green’s function approach also yields a physical interpretation of the exchange and correlation contributions to the theory. |
Tuesday, March 5, 2019 10:36AM - 10:48AM |
E20.00012: Real time-TDDFT study of thermal and non-thermal lattice dynamics depending on laser pulse-width Yoshiyuki Miyamoto In this work, I will discuss lattice dynamics of α-quartz conducted by femtosecond laser by performing the real-time TDDFT Ehrenfest dynamics with use of plane-wave basis set, TM type pseudopotentials, and adiabatic LDA functional. The α-quartz was expressed by a slab model with hydrogen termination. The distribution of kinetic energy for silicon and oxygen atoms was found to be nearly equal under shinning the femtosecond laser with full-width of half-maximum (FWHM) 100 fs, wave length 800 nm, and fluence 10 J/cm2. It is therefore concluded that this pulse width gave thermal dynamics on the lattice. By fixing the wave length and fluence of the femtosecond laser, the lattice dynamics with shorter FWHM was examined and non-equal distribution of kinetic energies among silicon and oxygen atoms was found. Furthermore, shorter pulse with FWHM=10 fs conducted ablation. I will discuss the physics behind this phenomenon. |
Tuesday, March 5, 2019 10:48AM - 11:00AM |
E20.00013: Non-linear effects in core photoemission from Real-time TDDFT. Marilena Tzavala, Joshua Kas, John Rehr, Lucia Reining In core photoemission spectroscopy a photon is absorbed and a core electron is emitted into the continuum, leaving behind a core hole. The remainder of the system responds to screen the core hole, significantly affecting the spectrum. State-of-the-art many-body perturbation theory (MBPT) methods such as the GW and the cumulant expansion are usually evaluated in the linear-response approximation. This requires a weak core hole; if this is not the case, one needs to go beyond linear response. This can be carried out with a non-linear cumulant derived in a MBPT framework, and evaluated from a real-time time-dependent density functional theory (TDDFT) approach. We discuss the application of this method with calculations carried out with an extension of our RT-Siesta code [1] for systems with d- and f valence electrons. |
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