Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session B16: Theory and Numeric Simulations of Glasses |
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Sponsoring Units: DSOFT GSNP Chair: Robert Dennis, University of Pennsylvania and Syracuse University Room: Room 208 |
Monday, March 6, 2023 11:30AM - 11:42AM |
B16.00001: Molecular simulations and hydrodynamic theory of nonlocal shear stress correlations in supercooled fluids and glasses Joerg Rottler, David Steffen, Ludwig Schneider, Marcus Mueller A supercooled fluid close to the glass transition develops nonlocal shear stress correlations that anticipate the emergence of elasticity. We performed molecular dynamics simulations of a binary Lennard-Jones mixture at different temperatures and investigated the spatiotemporal autocorrelation function of the shear stress for different wavevectors, q, from a locally measured and Fourier-transformed stress tensor. Anisotropic correlations are observed at non-zero wavevectors, exhibiting strongly damped oscillations with a characteristic frequency ω(q). A comparison with a recently developed hydrodynamic theory [Maier et al., Phys. Rev. Lett. 119, 265701 (2017)] shows a remarkably good quantitative agreement between the particle-based simulations and the theoretical predictions. |
Monday, March 6, 2023 11:42AM - 11:54AM |
B16.00002: Analysis of orientational autocorrelation in model glass forming system using MD simulation Jack Yungbluth, James M Caruthers, Grigori A Medvedev, Brett M Savoie The super-Arrhenian temperature dependence of mobility in glass forming materials is but one of several long-standing problems in condensed matter physics. Equally as intriguing is the origin of the α- and β-relaxation processes and the broadness of the relaxation spectrum. It is hoped that the molecular simulations can provide significant insight and yet there are surprisingly few studies of the relaxation spectrum as compared to the temperature dependence. We perform an MD study of a model system of molecular dumbbells, where the relaxation spectrum is extracted from the decay of the orientational autocorrelation functions P1 and P2, that is the Legendre polynomials of the cosine of the angle of rotation of molecular axis. The autocorrelation functions are analyzed with the Prony series, where both α- and β-relaxation processes are well resolved. The α-process is single-exponential at high temperature but broadens as the temperature decreases. We identify the molecular level events that accompany the broadening of the spectrum. The implications of the emerging picture of the molecular motions for the theory of the glass transition will be discussed. |
Monday, March 6, 2023 11:54AM - 12:06PM |
B16.00003: Facilitation governs the fate of nuclei in the equilibration of glasses Rahul N Chacko, François P Landes, Giulio Biroli, Olivier Dauchot, Andrea J Liu, David Reichman For glasses relaxing towards a low-temperature supercooled liquid, it has been claimed that equilibration proceeds via a crystallisation-like process of nucleation and domain growth of a dense disordered state. Similarly, a recent theoretical explanation for the melt fronts seen in the melting of ultrastable glasses is couched in terms of proximity to a first-order thermodynamic transition. In this talk, we present in-silico experiments that challenge these ideas. We artificially seed a nucleus and characterise its evolution during the equilibration of a heated or cooled glass towards a supercooled liquid. We find that upon cooling, a pre-equilibrated nucleus in fact shrinks. Upon heating, melt fronts are only obtained for extremely strongly annealed glasses, with front growth proceeding much more slowly than the ballistic growth seen in simple models of crystal melting. We argue that both of these features are consistent with a picture in which facilitation plays the dominant role in the equilibration dynamics of glasses. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B16.00004: Novel Experimental Method to Measure the Static Correlations in Supercooled Molecular Glass-forming Liquids Rajsekhar Das, Bhanu Prasad Bhowmik, Anand Balan Puthirath, Tharangattu N. Narayanan, Smarajit Karmakar Enormous enhancement in the viscosity of a liquid near its glass transition is generally connected to the growing many-body static correlations near the transition, often coined as ‘amorphous ordering’. Estimating the length scales of such correlations in different glass-forming liquids is highly important to unravel the physics of glass formation. Experiments on molecular glass-forming liquids become pivotal in this scenario as the viscosity grows several folds (∼ 1014), and simulations or colloidal glass experiments fail to access the long-time scales required. Here we design an experiment to extract the static length scales in molecular liquids using dilute amounts of another large molecule as a pinning site. Results from dielectric relaxation experiments on supercooled glycerol with different pinning concentrations of sorbitol and Glucose as well as the simulations on a few model glass-forming liquids with pinning sites indicates the robustness of the proposed method, opening a plethora of opportunity to study the physics of glass transition in other molecular liquids. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B16.00005: Mechanism of deformation in metallic glasses: Is the concept of defects useful? Charles K Lieou, Takeshi Egami It is known that deformation in disordered materials such as metallic glasses and supercooled liquids occurs via the cooperative rearrangement of atoms or constituent particles at dynamical heterogeneities, commonly regarded as point-like defects. We show via molecular-dynamics simulations that there is no apparent relationship between atomic rearrangements and the local atomic environment as measured by the atomic-level stresses, kinetic and potential energies, and the per-atom Voronoi volume. In addition, there is only a weak correlation between atomic rearrangements and the largest and smallest eigenvalues of the dynamical matrix. Our results confirm the transient nature of dynamical heterogeneities and suggest that the notion of defects may be less relevant than that of a propensity for rearrangement. |
Monday, March 6, 2023 12:30PM - 12:42PM |
B16.00006: Generation and Structural Characterization of Stealthy Hyperuniform Many-Particle Systems Peter K Morse, Paul J Steinhardt, Salvatore Torquato Hyperuniform many-particle systems are characterized by an anomalous suppression of large-scale density fluctuations compared to typical disordered systems (e.g., liquids) [1]. This classification includes crystals, quasicrystals and exotic amorphous systems. Disordered hyperuniform systems are now known to arise in a variety of contexts in physics, mathematics and biology. Stealthy hyperuniform systems represent the strongest form of hyperuniformity as they suppress single scattering events from infinite wavelengths down to intermediate wavelengths and are endowed with novel physical properties [2]. It has been shown that stealthy hyperuniform systems can be generated as the ground states of soft bounded pair interactions using the so-called collective-coordinate optimization scheme; see Ref. 2 and references therein. While considerable progress has been made in the generation and structural characterization of such systems, there are many open questions concerning the precise nature of the ground-state manifold and the phase transition from disordered to ordered states as a function of the stealthiness parameter. We shed light on these issues using the collective-coordinate approach for stealthy hyperuniform systems across Euclidean space dimensions. |
Monday, March 6, 2023 12:42PM - 12:54PM |
B16.00007: Unification of temperature dependence of mobility in the Arrhenian and super-Arrhenian region Jack Yungbluth, Grigori A Medvedev, Brett M Savoie, James M Caruthers A long-standing unsolved problem in condensed matter physics is a fundamental understanding of the temperature dependence of the relaxation time of glass forming materials. Experimentally, the log a mobility as a function of temperature shows two distinct regimes above and below Tα, one Arrhenian and the other super-Arrhenian, respectively. The change in the temperature response of the mobility at Tα suggests a structural change in the material which must affect other properties of the system. Using molecular dynamics simulations, a search for other physical quantities that change behavior at Tα has been carried out on three different model glass forming systems. Several molecular descriptors which change their temperature dependence at Tα have been identified, including the mean squared force applied to a molecule. We propose a mapping between these descriptors and log a that results in the linearization of the log a data across the entire range, including both the Arrhenian and super-Arrhenian regions. The conclusion holds for all model glass forming systems investigated, including a binary LJ mixture, LJ dumbbells and a coarse-grained OTP model. |
Monday, March 6, 2023 12:54PM - 1:06PM |
B16.00008: Temperature and driving rate effects on the yielding transition of amorphous solids Daniel J Korchinski, Joerg Rottler Abstract: (1154/1300) |
Monday, March 6, 2023 1:06PM - 1:18PM |
B16.00009: Burrowing dynamics of magnetoelastic robots in shallow granular beds Animesh Biswas, Balaram Desai, Max Moss, Arshad Kudrolli
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Monday, March 6, 2023 1:18PM - 1:30PM |
B16.00010: Model-free tracking control of regular and chaotic trajectories with machine learning Zheng-Meng n Zhai, Ying-Cheng Lai, Mohammadamin Moradi, Ling-Wei Kong Nonlinear tracking control is fundamental to robotics with a variety of civil and defense applications, the aim of which is to design a control law such that the output of the closed-loop system tracks a given reference signal. In traditional control engineering, designing tracking control requires complete knowledge of the system model and equations. While a problem of great current interest, developing model-free tracking control to track any desired trajectory, regular or chaotic, has remained to be a significant challenge. Here, by exploiting machine learning, we articulate a completely model-free framework to control a two-arm robotic manipulator, where the control objective is to track both simple and complicated trajectories, e.g., periodic and chaotic trajectories, as desired by using only partially observed states. In particular, we employ reservoir computing, a class of recurrent neural networks, as the controller and conduct the training via uniform noise as the control input, through which the reservoir-computing controller learns a mapping between the state error and a suitable control signal. In the testing phase, given the current and desired states, the reservoir controller generates the control signal that enables the robotic manipulator to track any desired trajectories, regular or chaotic. We demonstrate the robustness of our machine-learning based tracking control against measurement noise, disturbances, and uncertainties. |
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