Bulletin of the American Physical Society
APS April Meeting 2020
Volume 65, Number 2
Saturday–Tuesday, April 18–21, 2020; Washington D.C.
Session Y14: Computational Physics IIOn Demand
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Sponsoring Units: DCOMP Chair: Amy Liu, Georgetown University Room: Virginia A |
(Author Not Attending)
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Y14.00001: Thermal boundary conductance of beyond graphene two-dimensional materials Cameron Foss, Zlatan Aksamija An ongoing concern for 2D materials is their ability to thermally couple with their underlying substrate which acts as the primary pathway for heat removal in 2D devices. The thermal pathway from the 2D layer to substrate has been studied rigorously in graphene and various transition metal dichalcogenides. However, the literature still lacks a comprehensive analysis of thermal boundary conductance (TBC) for beyond-graphene materials. Previously [2D Mater. 6 (2019) 025019] we have shown that the TBC depends strongly on the overlap of available phonon modes in the long-wavelength regime and found selection criteria for choosing the best substrate for TBC. Here we use a combination of first-principles calculations and phonon interface transport modeling to calculate the TBC of several beyond-graphene 2D materials, such as; silicene, germanene, stanene, BAs, GaAs, InAs, and blue and black phosphorene, on amorphous and crystalline substrates. Our results show the TBC for these 2D materials on amorphous SiO$_{\mathrm{2}}$ (a-SiO$_{\mathrm{2}})$ falls between 20-50 MW.m$^{\mathrm{-2}}$.K$^{\mathrm{-1}}$, with the highest TBC being found in BAs due to its extremely flat ZA branch lending to a large low-energy density of states. A trend emerges that 2D materials with lower ZA branch frequencies have higher TBCs when placed on a-SiO$_{\mathrm{2}}$. Our results provide selection criteria for 2D materials that improve interfacial heat transport in 2D devices with amorphous and crystalline substrates. [Preview Abstract] |
Tuesday, April 21, 2020 1:42PM - 1:54PM |
Y14.00002: Intrinsically Localized Lattice Vibrations in Crystalline Lattices. Benjamin Agyare We examined the formation of Intrinsically Localized Modes (ILMs) for a pair of harmonic phonons along the direction [111] of the Sodium Iodide (NaI) crystalline lattice. The tendency for ILMs to form at a certain center-of-mass momentum q and corresponding relative momentum vector k is attributed to the van-Hove singularities condition in the non-interaction two-phonon density of states continuum. We observed that, as q converges to the high-symmetry point L$=$q ($\pi $, $\pi $, $\pi )$ of the Brillouin zone, the relative momentum vector k remains invariant at k($\pi $/2, $\pi $/2, $\pi $/2) for a certain threshold value of q, and coalesces at the upper-edge of the two-phonon density of states spectrum with high degeneracy in the two-phonon critical energy. We conclude that the excitation spectra of the pairs of harmonic phonon excitations become energetically degenerate past the threshold q value towards L at the invariant vector k, announcing the strong presence of ILMs. The calculated ILMs were observed at critical energies of 20.0 meV and 25.0 meV for the spring coupling constants ratios 0.598 and 0.202 respectively. Reports of Inelastic Neutron Scattering experiments have identified one-phonon breather excitations energy of 10.2 meV at elevated temperatures of 555 K. The formation of ILMs, or multi-phonon bound states, is expected to arise as a result of the anharmonic interactions that lift these degeneracies to enhance the formation of ILMs. [Preview Abstract] |
Tuesday, April 21, 2020 1:54PM - 2:06PM |
Y14.00003: Modeling Exciton Transport in the Photosystem II Reaction Center via the Modified Generalized Quantum Master Equation Kristina Lenn, Ellen Mulvihill, Xing Gao, Alexander Schubert, Eitan Geva Organic solar cell materials are a cheaper option to traditional silicon but lack the efficiency for which silicon is famous. Quantum computers can outperform the greatest supercomputer, but the short-lived coherences lead to classical-like behavior. Light-harvesting systems (LHS) serve as an example to both applications. LHSs absorb sunlight and convert it into an electrochemical gradient with near unity quantum efficiency and maintain long coherence times. Probing the exciton dynamics of these systems, one of which is the Photosystem II reaction center (PSII RC), can elucidate how these systems are able to transport excitons with approximately 99% efficiency. This revelation could propel solar-cell and quantum-computing research forward at unprecedented levels. To do this, we have employed a projection-free version of the Generalized Quantum Master Equation (GQME) whose memory kernel is calculated using approximate methods, such as the Mean-Field Approximation (MFA) and the Linearized Semiclassical Method (LSC). This approach, verified against a Spin-Boson model and the well-studied LHS Fenna-Matthews-Olson (FMO) complex, is more computationally efficient and yields a high level of accuracy compared to exact methods such as the Quasi-Adiabatic Propagator Path Integral (QuAPI [Preview Abstract] |
Tuesday, April 21, 2020 2:06PM - 2:18PM On Demand |
Y14.00004: Numerical construction of Non-Abelian vortices in holographic superconductors Adam Peterson, Roberto Auzzi, Gianni Tallarita I discuss our recent work on the construction and analysis of non-Abelian vortices in a holographic superconductor. I will begin with a short introduction to the AdS/CFT correspondence in the context of condensed matter systems. I will then present the underlying theory and discuss the computational approach to constructing vortex solutions of the Einstein equations. Using these solutions I will discuss their interpretation from the thermodynamic potentials in the holographic dual description and determine some properties of a strongly coupled superconductor. If time permits I will offer a brief discussion on the interaction of these vortices with the low energy excitations in the model. [Preview Abstract] |
Tuesday, April 21, 2020 2:18PM - 2:30PM On Demand |
Y14.00005: Parallel Adapative Monte Carlo Optimization, Sampling, and Integration in C/C++, Fortran, MATLAB, and Python Shashank Kumbhare, Amir Shahmoradi At the foundation of predictive science lies the scientific methodology, which involves multiple steps of observational data collection, developing testable hypotheses, and making predictions. Once a scientific theory is developed, it can be cast into a mathematical model whose parameters have to be fit via observational data. This leads to the formulation of a mathematical objective function for the problem at hand, which has to be then optimized to find the best-fit parameters of the model or sampled to quantify the uncertainties associated with the parameters, or integrated to assess the performance of the model. Toward this goal, a highly customizable, user-friendly high-performance parallel Monte Carlo optimizer, sampler, and integrator library is presented here, which can be used on a variety of platforms with single to many-core processors, with interfaces to popular programming languages including C/C++, Fortran, MATLAB, and Python. [Preview Abstract] |
Tuesday, April 21, 2020 2:30PM - 2:42PM On Demand |
Y14.00006: Optimization of an axial injection plasma torch using numerical analysis Ilker Uzun-Kaymak, Giray Mecit, Devrim Ozdemir, Ece I. Sungur Axial Injection plasma torch is a surfaguide microwave plasma source operated at 2.45 GHz. The system can operate at power settings up to 2kW. The plasma is formed inside a 20mm diameter quartz tube using Argon gas. The aim of this study is to understand and optimize the plasma flow characteristics for the purpose of the material interactions. The experimental setup is modeled using COMSOL Multiphysics\textregistered Computational Fluid Dynamics Module. The geometry of the flow can be altered using nozzle extensions. Meanwhile different microwave power settings alter the gas temperature hence the viscosity. Images from the plasma torch are captured via Z type Schlieren imaging. It has been observed that the higher mass flow rates require a turbulent model. Reynolds Averaged Naiver Stokes (RANS) and Large Eddy Simulation (LES) approaches are compared with the real data. Simulations are conducted using parameter sweeping at different flow rates. In addition to the COMSOL Multiphysics\textregistered we are also developing our Python code using libraries from the FEniCS project. The aim is to find critical limits of the geometry and flow for the plasma jet to be effectively used in material processing. [Preview Abstract] |
Tuesday, April 21, 2020 2:42PM - 2:54PM On Demand |
Y14.00007: Simulation and Visualization of the Predictable Parts of the Schrodinger Cat Experiment. Godfrey Akpojotor The parts when the poison is released and its effects in the Schrodinger Cat experiment are modeled in this study as a simple harmonic oscillator using the usual various steps of modeling. The emerging second order differential equation with constant coefficients has three key components: the damping constant, b which is the amount of poison the cat is exposed to, the spring constant, k, which is the pumping of the blood in the cat's heart and the mass, m of the cat. Python codes and VPython codes were then used to resolve the differential equation to obtain both the numerical and simulated results. It is observed in both results that by varying the amount of poison, pumping of the blood in the heart and the mass of the cat, one can predict the following three states: (a) underdose: producing normal sinusoidal motion (b) critical dose: producing abnormal sinusoidal motion and (c) overdose: producing quenched sinusoidal motion. [Preview Abstract] |
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