Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session B45: Understanding glasses and disordered systems through computational models IIFocus
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Sponsoring Units: DCOMP DSOFT GSNP DPOLY Chair: Joerg Rottler, University of British Columbia Room: 706 |
Monday, March 2, 2020 11:15AM - 11:51AM |
B45.00001: Sound Scattering and Plasticity n Amorphous materials Invited Speaker: Anne Tanguy Plastic deformation in amorphous materials results from a succession of local irreversible rearrangements at the nanometric scale known as Transformation Zones. From a numerical point of view, these Transformation Zones are well described within the theory of Eshelby inclusions. In this talk, we will compare sound scattering in amorphous materials in the presence of inclusions. We first remind the signature of structural disorder on acoustic attenuation. We will then detail the role of heterogeneous elastic inclusions on sound attenuation and thermal transfers. Finally we will focus on the effect of Eshelby like inclusions on sound attenuation. |
Monday, March 2, 2020 11:51AM - 12:03PM |
B45.00002: Energy Dissipation in Amorphous Solids during Elastic Deformation Jan Grießer, Lars Pastewka Excitation of atomic vibrational modes is an important mechanism for energy dissipation in friction phenomena. In crystalline materials, the vibrational modes can be represented as plane waves, i.e. the phonons. This is in general not possible in amorphous solids due to structural disorder, which gives rise to different types of vibrational modes. Energy dissipation is related to the lifetime of these vibrational modes. Here we use large-scale molecular dynamics simulations to investigate energy dissipation mechanisms in a model amorphous solid and compare it to a crystalline solid. While the lifetimes of phonons show universal scaling ω-2 in the limit of low frequencies ω, vibrational modes in the amorphous system show different scaling that depends on the type of the vibrational mode. We also carry out cyclic deformation of the amorphous solid in the elastic regime. In this limit, energy dissipation can be traced back to non-affine deformation. We demonstrate that the energy dissipation can be predicted by knowledge of the lifetimes and the non-affine displacement field. |
Monday, March 2, 2020 12:03PM - 12:15PM |
B45.00003: Local excitations in re-heated ultrastable glasses WENCHENG JI, Tom W. J. de Geus, Marko Popović, Edan Lerner, Matthieu Wyart Quasilocalised modes are local excitations present at low frequency vibrational spectrum in glasses. We numerically study their frequency density Dloc(ω) evolution under thermal cycles at different temperatures T, starting from ultrastable glass configurations where these excitations are gapped. The latter are prepared by an algorithm where individual particles can "breathe", modelling the effect of the swap algorithm in a grand-canonical ensemble. We find that a quartic behavior Dloc(ω)=A4 ω4 always appears at any finite T. The prefactor A4, which characterizes the number of quasilocalised modes, can increase by a factor of thousands with growing T in our numerical observations. Moreover at small T, A4 follows an Arrhenius behaviour: A4 ~ exp(-Ea/T) where Ea is atypical energy that depends on the magnitude of the gap initially present. We provide arguments for this dependence. Overall, our result support that true gaps never exists at finite temperature in finite dimensions, and suggest that in some equilibrated super-cooled liquids A4 may decrease exponentially at low T. |
Monday, March 2, 2020 12:15PM - 12:27PM |
B45.00004: Cluster-flip colloidal and atomistic algorithms with background potentials Jaron Kent-Dobias, James Patarasp Sethna We introduce an extension to cluster algorithms of colloidal and atomistic models that naturally incorporates nonuniform background potentials. Simulations of these systems are important for studying the statistical mechanics of fluids and myriad liquid, solid, and glassy phase transitions. Nonuniform background potentials like gravitational or trapping fields are typically present in experiments and can reveal new features of the statistical mechanics at play due to, e.g., nonuniform chemical potential. This method takes existing cluster methods and incorporates background potentials without adding a rejection step by treating the orientation of the system as a dynamical degree of freedom. We assess its efficiency in several applications and explore connections with the celebrated swap Monte Carlo for glasses. |
Monday, March 2, 2020 12:27PM - 12:39PM |
B45.00005: Accelerated relaxation in amorphous materials under cyclic loading with alternating shear orientation Nikolai Priezjev The effect of alternating shear orientation during cyclic loading on the relaxation dynamics in disordered solids is examined using molecular dynamics simulations. The model glass was initially prepared by rapid cooling from the liquid state and then subjected to cyclic shear along a single plane or periodically alternated in two or three dimensions. We showed that with increasing strain amplitude in the elastic range, the system is relocated to deeper energy minima. Remarkably, it was found that each additional alternation of the shear orientation in the deformation protocol brings the glass to lower energy states. The results of mechanical tests after more than a thousand shear cycles indicate that cyclic loading leads to the increase in strength and shear-modulus anisotropy. |
Monday, March 2, 2020 12:39PM - 12:51PM |
B45.00006: Mesoscale models of amorphous solids under cyclic shear: emergence and character of limit cycles. Kareem Abdelshafy, Botond Tyukodi, Damien Vandembroucq, Craig E Maloney Amorphous solids (amorphous metallic alloys, glassy polymers, foams, emulsions, pastes, compressed granular packings, etc.) respond in complex ways to imposed shear. In steady shear, the response depends on preparation and shear may or may not localize upon yielding. In cyclic shear, if the amplitude of cycling remains below the yielding threshold, the system may either exhaust all plastic behavior and become purely elastic, or lock into a periodic orbit where plasticity is reversed after one or many cycles and the system returns to its previous configuration. These complex limit cycles have been observed in experiments and particle-based simulations. Here, we show that a simple mesoscale model which treats the material as a mosaic of yielding plaquettes is able to capture the complex limit cycles with orders of magnitude less computational time than particle-scale models. We use the mesoscale model to study the limit cycles at various strain amplitude. |
Monday, March 2, 2020 12:51PM - 1:03PM |
B45.00007: Comparison of yielding behaviour in model network and atomic glasses Himangsu Bhaumik, Giuseppe Foffi, Srikanth Sastry Yielding in a model atomic glass (Kob-Andersen binary mixture) has been studied recently through athermal quasi-static shear deformations [1], revealing a sharp yielding transition accompanied by strain localisation [2]. We investigate the manner in which such a transition is manifested in a model network glass, the BKS model of silica [3]. Silica exhibits a fragile-to-strong cross over a function of temperature, and we investigate the manner in which yielding and the accompanying strain localisation differs in glasses prepared initially in the strong and fragile regimes. We find qualitative differences in the yielding behaviour, and in the details of structural changes accompanying yielding. We compare these results to the aforementioned atomic glass with comparable changes in the degree of annealing, and recent results regarding the effect of annealing in the yielding behaviour of glasses [4]. |
Monday, March 2, 2020 1:03PM - 1:15PM |
B45.00008: Molecular Dynamics Study on Mechanical and Rheological Properties of Bulk Metallic Glass around Glass Transition Temperature Ji Woong Yu, S. H. Ebrahimnazhad Rahbari, Won Bo Lee Bulk Metallic Glasses (BMG) or amorphous alloys usually contain more than two kinds of atoms. These materials have been central in both material engineering and material physics ever since their first appearance in 1960s, and posses superior material properties (e.g. tensile yield stress). However, the mechanical properties of BMG are not well understood due to nonequilibrium nature of the glass transition, and dramatic slow-down of the dynamics around the glass transition temperature. Using large scale computational power, we investigated the mechanical properties of the celebrated Kob-Andersen mixture, a model BMG, using active microrheology in molecular dynamics (MD) simulations. Moreover, we systematically compared results of the active microrheology with those obtained from global shearing. With strong evidence, we conclude superiority of the either method. |
Monday, March 2, 2020 1:15PM - 1:27PM |
B45.00009: Computational generation of voids in a-Si and a-Si:H by cavitation at low density Enrique Guerrero, David Strubbe Hydrogenated amorphous Si (a-Si:H) has seen a renewed interest for its application in heterojunction with intrinsic thin-layer (HIT) solar cells. Known deficiencies in this material’s photovoltaic properties are limited hole mobilities and the Staebler-Wronski effect, a light-induced degradation of efficiency which may be in part due to voids within the structure. Simulations of voids in a-Si typically involve atomic removal, but these methods require an a priori idea of the bonding structure near the void. Instead, we generate voids within a-Si and a-Si:H using a fast, unbiased approach: the Wooten-Winer-Weaire classical-potential Monte Carlo method where we vary the density and replace some Si-Si bonds with Si-H bonds. At low density, voids form (like cavitation in a liquid), maintaining 4-coordination but increasing bond angle deviation, reducing medium-range order, and altering local stricture within 4 Å of the void. This work provides a set of void structures for further studies of their effects on degradation, hole mobility, two-level systems, thermal transport, and elastic properties. (ArXiv: 1907.01327) |
Monday, March 2, 2020 1:27PM - 1:39PM |
B45.00010: Molecular Dynamics Simulation of Amorphous Oxides Rui Zhang, Jun Jiang, Maher Yazback, Alec Mishkin, Hai-Ping Cheng Amorphous oxides has been used as coating material of interferometers for gravitational wave detection. To optimize their performance, efforts have been devoted to determining diffusive behavior of amorphous pure Ta2O5 as well as Ta2O5 with various dopants by classical molecular dynamics (MD) simulations. Furthermore, empirical pair potentials aiming at reproducing elastic properties of GeO2 and doped GeO2 have been constructed. The new potentials are applied to examine the thermodynamic properties of such material. Also, the vibrational density of states and Raman spectra of amorphous oxides have been demonstrated using MD simulation. |
Monday, March 2, 2020 1:39PM - 1:51PM |
B45.00011: Transient Structured Fluctuations Approaching 2D Kagome-Liquid Transition Linsey Nowack, Stuart A Rice We study two 2D systems known to support an open-packed Kagome phase[1]. Both systems have repulsive pair potentials, one designed by Piñeros, Baldea, and Truskett and another by Zhang, Stillinger, and Torquato[2-3]. Using the aperture cross-correlation function (ACCF), we identify structured fluctuations in the liquid phases approaching the Kagome-liquid transition[4]. These Kagome-like fluctuations may be distinguished from hexagonal ones by calculating the ACCF at two different wavevector magnitudes along the second diffraction ring. Fluctuations near a string-Kagome transition involve transient structures that are different for different potentials. We find congruencies in the sequence of phases along an isotherm for many different 2D systems of Hertzian, Lennard-Jones-Yukawa, Core-Corona, and Daoud–Cotton particle potentials. These similarities suggest a universal mechanism among the phase transitions of 2D systems supported by central repulsive potentials. |
Monday, March 2, 2020 1:51PM - 2:03PM |
B45.00012: Analysis of coarsening and aging in Ising spin glasses using record dynamics Stefan Boettcher, Mahajabin Rahman Record Dynamics (RD) describes the ubiquitous relaxation phenomenology known as "aging" that ensues after a hard quench in terms of a log-Poisson process. According to RD, a nonequilibrium system after a quench relies on fluctuations that randomly generate a sequence of irreversible record-sized events (quakes or avalanches) that allow the system to escape ever-higher barriers of meta-stable states within a complex energy landscape. Only the activation over such barriers allows the system to relax while tumbling into the next meta-basin that is marginally more stable. Within this picture of RD, a clear distinction can be drawn between the coarsening dynamics of, say, an Ising ferromagnet and the aging of the spin glass, which are often put in the same category. To that end, we use Ising spin models that interpolate between the spin glass and ferromagnet by varying the admixture of anti-ferromagnetic bonds from 50% to zero. Indeed, the accumulation of record events grows logarithmically with time in the glassy regime, with a sharp transition at a specific admixture in the ferromagnetic regime where such activations saturate quickly. We show this effect both for the Edwards-Anderson model on a cubic lattice as well as the Sherrington-Kirkpatrick (mean-field) spin glass. |
Monday, March 2, 2020 2:03PM - 2:15PM |
B45.00013: Many-body localization to spin glass phase transition in disordered spin-chain system Zeyang Li, Pai Peng Disorder in a strongly correlated spin-chain system can give rise to novel phases of matter, such as many-body localization (MBL) phases or spin-glass (SG) phases. The two phases share similar non-thermalizing properties due to the existence of extensive set of local integrals of motion (LIOMs), and the SG phases feature in other properties such as a SG order parameter as well as the doubly degenerate eigenstates. |
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