Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session W02: Materials in Extremes: Simulations of Materials at Extreme ConditionsFocus
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Sponsoring Units: GSCCM Chair: Anatoly Belonoshko, KTH Royal Inst of Tech Room: 105 |
Friday, March 6, 2020 8:00AM - 8:12AM |
W02.00001: Force-based interatomic potential for strength and toughness in brittle solids Md Hossain Most of the available potentials (such as Tersoff, Stillinger-Weber, ReaxFF, EDIP, Vashishta, etc.) produce reliable properties (such as bulk modulus) of a solid under symmetry-preserving deformation or symmetry-breaking deformation around the linear regime of mechanical deformation. However, despite the incorporation of long-range interactions, they have sizable accuracies in producing extreme mechanical properties such as strength and toughness (which are two critical extreme mechanical properties of a solid). To address the limitations, we developed a force-based scheme that gives first-principles accurate strength and toughness. We validated the approach for a number of brittle solids including diamond, SiC, hBN, and graphene. In addition to fitting the equilibrium material properties, the approach allows fitting the potential to the forcing behavior as well as the mechanical strength of the solid, without requiring any ad hoc modifications of the nearest-neighbor interactions to avoid artificial stiffening at larger deformation. The talk will discuss the development of the force-based scheme and its application for a number of brittle solids. It will highlight a number of failure mechanisms that emerge from an accurate description of the interatomic interactions. |
Friday, March 6, 2020 8:12AM - 8:24AM |
W02.00002: Automated generation of machine learning-based atomistic potentials for extreme conditions Ben Nebgen, Justin Smith, Nithin Mathew, Jie Chen, Leonid Burakovsky, Saryu Fensin, Kipton Barros Neural Network (NN) interatomic potentials are a powerful tool for atomistic scale simulations, combining the generality and accuracy of ab-initio methods with costs approaching those of classical potentials. A robust training dataset covering many atomic configurations must be computed with ab-initio methods to train an accurate NN potential. Recently, active learning (AL) algorithms have demonstrated the ability to generate training datasets quickly and efficiently by selecting atomic configurations for which a NN potential has high uncertainty. This facilitates the generation of training datasets through a minimum number of ab-initio calculations with little or no human intervention. A LAMMPS interface for our NN potential, named ANI, has facilitated large-scale GPU-accelerated MD simulations using domain decomposition. Utilizing this interface, we validate an autonomously generated ANI aluminum potential using both static and dynamic simulated properties, including a partial phase diagram. Additionally, we present million-atom shock simulations of aluminum to illustrate robustness and demonstrate extensibility to the prediction of high-pressure phases. |
Friday, March 6, 2020 8:24AM - 8:36AM |
W02.00003: Quantum-accurate SNAP Potential For Large-Scale Molecular Dynamics Simulations of Carbon at Extreme Conditions Jonathan T Willman, Ashley Williams, Kien Nguyen-Cong, Anatoly Belonoshko, Mitchell Wood, Aidan Thompson, Ivan Oleynik Highly accurate interatomic potentials are of critical importance for trustworthy MD simulations of materials at extreme conditions of high pressures, temperatures, and high strain-rates. A new quantum accurate Spectral Neighbor Analysis Potential (SNAP) for carbon has been developed to describe the behavior of carbon at multi-megabar pressures and up to 10,000 K. SNAP is formulated in terms of the bispectrum components, which play a role of descriptors that characterize the local neighborhood of each atom. Machine learning is used to train the quadratic SNAP on a large set of first-principles training data. The SNAP development involves (1) the generation of the training database comprising a consistent and meaningful set of first-principles DFT data; (2) the robust and physically guided fit of SNAP parameters; and (3) the validation of the SNAP potential in simulations of carbon at extreme conditions. In this presentation, several applications of SNAP to study carbon at extreme conditions are described. |
Friday, March 6, 2020 8:36AM - 8:48AM |
W02.00004: Time dependent boundary conditions for large scale atomistic simulations of shocked surface instabilities James Hammerberg, Ramon Jose Ravelo, Timothy Germann
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Friday, March 6, 2020 8:48AM - 9:00AM |
W02.00005: Molecular dynamics simulation of shock compressed cis-polybutadiene : from in situ synthesis to mechanical analyses of long-term relaxation processes Gautier Lecoutre, Claire Lemarchand, Laurent Soulard, Nicolas Pineau We used a recently devised procedure based on molecular dynamics to generate cis-polybutadiene melts with various chain lengths [1] and study their mechanical behaviour under shock compression with the non-reactive OPLS all-atom force-field. The resulting samples show properties in excellent agreement with previous works [2] with negligble influence of the chain length. Comparison of direct shock with shock equilibrium (hugoniostat) simulations shows a discrepancy in the shear stresses. Based on a careful mechanical analysis of the time-dependance of this difference behind the shock front, we show that their timescale is compatible with the typical equilibrium relaxation times at play in these complexe materials. |
Friday, March 6, 2020 9:00AM - 9:12AM |
W02.00006: Structure and dynamics of liquid Fe at high pressure and temperature. A first principles study David J Gonzalez, Miriam Marques, Luis Gonzalez The static and dynamic properties of bulk liquid Fe at high pressure and temperature conditions have been studied by using first principles molecular dynamics simulations based on the density functional theory. Results are reported for some thermodynamic states resembling those found in the Earth's outer core. |
Friday, March 6, 2020 9:12AM - 9:24AM |
W02.00007: Extreme Dynamic Tension Theory: Preliminary Research Seokbin (Bin) Lim, Philipp Baldovi The dynamic tension fracture has brought much interests in various engineering applications ranging from the pressure vessel/pipe failure to the explosively driven fragmentations in the commercial/space or military applications. There has been great improvement in this area of study by many researchers, but the question regarding the fundamental mechanism of extreme tension remains unanswered. In this report, an extreme dynamic tension theory based on the conservation equations is proposed, and it is evaluated by a series of MD (molecular dynamic) and hydrocode simulations. In-depth descriptions of tension wave speed, wave profile, tension pressure/profile, particle velocity of the plastic tension wave, etc. are present, hoping to provide a clue to understand the extreme dynamic tension physics prior to the crack formation. |
Friday, March 6, 2020 9:24AM - 9:36AM |
W02.00008: Electron-Phonon Interactions in Condensed Phases under Compression Anguang Hu Electron-phonon interactions in condensed phases are central to all important temperature-dependent properties of materials such as electrical resistance in metals, carrier mobility in semiconductors, and phase transitions in conventional superconductors. Based on all-electron quantum solid-state chemistry using density functional theory, non-perturbative calculations of electron-phonon interactions have been recently developed in condensed phases under compression. Such calculations can provide a clear understanding on the thermal dependence of electron energy bands and thermomechanically induced distortion of band structures to raise or lower the Fermi level, leading to the generation of charge and spin density waves mainly determined by amplitudes of vibrational motion under mechanical compression. More importantly, calculations also show how vibrational mode energies in the measure by vibrational amplitudes distribute to reach an equilibrium state and even to create a superconducting state with the temperature-dependent energy gap. High-pressure superconductors H3S and LaH10 are taken as examples to show calculation results in comparison with experiments. |
Friday, March 6, 2020 9:36AM - 9:48AM |
W02.00009: Molecular simulations of ultrafast radiation induced melting at metal-semiconductor interfaces Ashwin Ravichandran, John Lawson Understanding radiation induced ultrafast melting at material interfaces is essential in designing robust electronic devices for aviation/space applications and in laser machining. While it is difficult to achieve the spatial and temporal resolution required to quantify the phenomenon experimentally, simulations can provide the detailed mechanisms of the structural changes that happen during phase transition. In this work, we use molecular simulations to study the effect of radiation damage on silicon carbide (SiC) - tungsten (W) interfaces which is of interest in high power electronics. A multi-scale approach is involved wherein the reactions at the interfaces are quantified using ab-initio molecular dynamics (MD) simulations and classical MD simulations are employed to understand the structural and diffusional changes across the material interface. Finally, coarse-grained Lennard-Jones type models are used to study the larger scale mechanisms and structures obtained due to the induced damages. We show that the response of the material to radiation damage depends on factors such as energy of the incident radiation, thermal properties, and molecular structure of the material. |
Friday, March 6, 2020 9:48AM - 10:00AM |
W02.00010: Accelerated Molecular Dynamics Simulations of Dislocation-Obstacle Interactions in Tungsten: Enabling Micro-Second Simulations Nithin Mathew, Enrique Martinez Saez, Danny Perez Plasma Facing Materials (PFMs) in fusion reactors have to withstand extreme temperatures and high particle flux of Hydrogen (H) isotopes and Helium (He). Tungsten (W) is the main candidate for PFM in the International Thermonuclear Experimental Reactor but He irradiation of W results in modification of surface microstructure due to creation of Helium-Vacancy (HenVm) complexes. This leads to increased retention of H isotopes and degradation of thermomechanical stability. In this work, we study the interaction of these HenVm complexes with edge dislocations using accelerated molecular dynamics. We use a novel Parallel Replica Dynamics method where states and transitions are identified on-the-fly using a diffusion distance metric calculated from an approximation of the Koopman operator of the dynamics. Using up to 600 replicas, we are able to investigate the interactions between edge dislocations and HenVm complexes at temperatures ranging from 300-1200 K and applied stresses well below the critical resolved shear stress. The calculated rates for the dislocation to overcome the obstacle span ≈3 orders of magnitude, reaching micro-second timescales at low temperatures/stresses, and show a strong dependence on the applied stress. |
Friday, March 6, 2020 10:00AM - 10:12AM |
W02.00011: Periodic Boundary Condition for Large Material Deformation Duan Zhang, Min Wang, Paul Barclay The use of periodic boundary conditions has been a common practice in numerical simulations for the study of constitutive response of materials. To consider material deformation, the common method of enforcing the periodic boundaries is to deform the computational domain with the material, which limits the strain of the material to order one. The method fails when strains are large or the deformation gradients are complicated, such as those containing large rotation or twist. For instance, it is quite difficulty to perform a simulation under a large pure shear deformation because of the distorted and elongated computational domain. |
Friday, March 6, 2020 10:12AM - 10:48AM |
W02.00012: Phase transitions and new states under extreme conditions from first-principles Invited Speaker: Jian Sun High pressure is an important method to modify the free energy surface of materials and overcome the barriers for synthesizing new functional materials. On the other hand, crystal structure search based on ab initio calculations has been successfully used to prediction new materials. In this talk, I will introduce some of our recent work on theoretical prediction on high pressure phase transitions, functional materials with interesting properties, and new states of matter under extreme conditions, such as superionic states. |
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