Computational Thermodynamics and Kinetics: Diffusion, Excitations and Rare Events I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Computational Materials Science and Engineering Committee
Program Organizers: Nana Ofori-Opoku, Canadian Nuclear Laboratories; Jorge Munoz, University of Texas at El Paso; Sara Kadkhodaei, University Of Illinois Chicago; Vahid Attari, Texas A&M University; James Morris, Ames Laboratory
Wednesday 8:30 AM
February 26, 2020
Room: 33C
Location: San Diego Convention Ctr
Session Chair: Marco Bernardi, California Institute of Technology; Chelsey Hargather, New Mexico Institute of Mining and Technology
8:30 AM Invited
Where do Thermodynamics and Transport Kinetics Meet?: Zi-Kui Liu1; Yi Wang1; Irina Belova2; Graeme Murch2; 1Pennsylvania State University; 2University of Newcastle
In flux equations, there are two terms: the driving forces defined by the independent potential gradients and the kinetic coefficients in front of the driving forces, with the former in the domain of thermodynamics, and the latter in the domain of kinetics. The connections between these two sets of properties are not commonly discussed. In this presentation, our studies on understanding and prediction of diffusion, thermotransport, and thermoelectric properties of materials will be presented. We will first discuss the prediction of tracer diffusion coefficients based on energetics along the diffusion path. In terms of thermoelectric property, we will demonstrate the correlation between electronic entropy and Seebeck coefficient. In terms of thermotransport property, we will evaluate the relationship between diffusion coefficient and heat of transport.
9:00 AM
Free Energy Calculation of Mechanically Unstable but Dynamically Stabilized Phases: Sara Kadkhodaei1; Axel van de Walle2; 1University of Illinois at Chicago; 2Brown University
The phase diagram of numerous materials of technological importance features high-symmetry high temperature phases that exhibit phonon instabilities. Leading examples include shape-memory alloys, as well as ferroelectric, refractory, and structural materials. The thermodynamics of these phases have proven challenging to handle by first-principles computational techniques due to the occurrence of constant anharmonicity-driven hopping between local low-symmetry distortions, while the system maintains a high-symmetry time-averaged structure. We present a novel method that efficiently explores the system’s ab-initio energy surfaceby discrete sampling of local minima, which is combined with a continuous sampling of the vicinity of these local minima via a constrained harmonic lattice dynamic approach. The calculated free energies for the austenite and martensite phases in NiTi and PtTi shape memory alloys are presented. Finally, we introduce an open-access and fully automated software toolkit of the presented method.
9:20 AM
A First-principles Investigation of the Importance of Various Calculation Parameters on Self-diffusion Coefficient Calculations in FCC Metals: John O'Connell1; Chelsey Hargather1; 1New Mexico Institute of Mining and Technology
Using first-principles calculations based on density functional theory to determine self-diffusion coefficients in metals has been an invaluable tool to the materials community, as diffusion is the primary mechanism of mass transfer in metals. As the materials community moves towards high-throughput or automated techniques for calculating properties of large materials data sets, understanding which parameters (vibrational method, supercell size, etc) have the most significant effect on diffusion properties is critical. In this work, diffusion parameters and thermodynamic properties of Ag, Cu, and Ni were found using first-principles calculations and the following variables: 32, 64, and 108 atom supercells, both the LDA and PBEsol exchange and correlation functionals, and two vibrational entropy calculation methods. Comparisons of the accuracy, computational expense, and necessity of each calculation parameter will be discussed in light of its effects on diffusion coefficients, vacancy concentration, and other thermodynamic properties.
9:40 AM Invited
Features of Defects Diffusion in Concentrated Alloys: Percolation, Sluggish and Chemically Biased Atomic Transport: Osetsky Yury1; Alexander Barashev2; Laurent Béland3; Yanwen Zhang1; 1Oak Ridge National Laboratory; 2University of Michigan; 3Queen's University
Concentrated single-phase solid solutions represent a new class of materials with fascinating properties many of which are attributed to the sluggish atomic-level diffusion and transport. The origin and controlling mechanisms of sluggish diffusion were recently studied for the case of point defect migration. We review the main results on atomistic modeling of diffusion via point defects migration in Ni-Fe model alloys. We have found that chemical properties and percolation effects lead to sluggish and chemically biased atomic transport. Moreover, adding a fast diffuser can result in significantly slower diffusion, going against simple assumptions. These mechanisms affect microstructure evolution under different and lead to a number of new phenomena such as segregation bias and formation new, sometime thermodynamically non-equilibrium, phases.This work was supported by the Energy Dissipation to Defect Evolution (EDDE), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.
10:10 AM Break
10:30 AM Invited
Advances in Computing Charge Carrier Dynamics and Electron Interactions from First Principles: Marco Bernardi1; 1California Institute of Technology
We briefly review advances in first-principles calculations that are enabling accurate predictions of charge carrier mobility and scattering mechanisms in a wide range of materials. We then focus on new approaches for computing electron-phonon interactions in materials with structural phase transitions (and lattice anharmonicity) and with electron-phonon interactions strong enough to form polarons. Including soft phonon modes and polarons allows us to accurately predict the electron mobility and its temperature dependence in SrTiO3, a prototypical perovskite oxide, while shedding new light on transport regimes beyond the quasiparticle scattering paradigm. Our progress on computing electron-defect and spin-phonon interactions from first principles is also discussed.
11:00 AM
State-dependent Force Constants for Anharmonicity: Jorge Munoz1; 1The University of Texas at El Paso
The computational study of thermodynamic properties from ab initio molecular dynamics (AIMD) is powerful but encumbered by expensive computation that limits the number of atoms and time steps. The temperature-dependent effective potential (TDEP) method provides a shortcut to the thermodynamics by fitting second- and higher-order force constants to AIMD simulations and has helped elucidate behaviors in materials that are beyond quasiharmonicity. In this talk I will introduce an alternative method to extract thermodynamics from molecular dynamics that assumes only harmonic potentials but whose force ‘constants’ depend on the state of the system, and uses a classifier to determine the state. While the curse of dimensionality is real in computational thermodynamics, the user can set the granularity of the classifier to specific needs, which determines how much data is needed for the fits. I will discuss advantages and disadvantages of the current method.
11:20 AM
The Temperature Dependence of Electron-phonon Interactions in Vanadium: Brent Fultz1; Fred Yang1; Olle Hellman1; 1California Institute of Technology
Vanadium is known for its electron-phonon interactions, which cause superconductivity at cryogenic temperatures. Electron-phonon interactions exist at much higher temperatures, however. We used first-principles calculations to study the Fermi surface of bcc vanadium at temperatures up to 1100 K. These calculations accounted for effects of thermal atom displacements on electronic energies. Band unfolding was used to project the spectral weight of the electron states into the Brillouin zone of a standard bcc unit cell. The calculated phonon dispersions showed thermal stiffening of their Kohn anomalies near the Gamma point, and showed thermal stiffening of the longitudinal phonons at the N point. An electronic topological transition (ETT, or Lifshitz transition) was discovered near the Gamma point. However, the effects of the ETT on phonon energies were overcome by the thermal smearing of the Fermi surface, which reduces the spanning vector densities of phonon modes.
11:40 AM
Thermal Properties of Disordered Alloys from Density Functional Theory Calculations: Pavel Korzhavyi1; 1KTH Royal Institute of Technology, Stockholm, Sweden
An efficient scheme is developed for a predictive modeling of thermal properties of metals and alloys on the basis of density functional theory (DFT) calculations. The scheme employs the Green's function approach to solving the electronic structure problem at a finite electronic temperature. The chemical and paramagnetic disorder in alloys are treated within the coherent potential approximation. The phonon contributions to the free energy are evaluated in the quasiharmonic Debye model parametrized using the elastic constants calculated as a function of volume and temperature. The efficiency of the developed computational scheme is demonstrated by computing the thermo-physical properties of Ti, Cr, Mn, Fe, Ni, and Nb metals and some of their alloys at temperatures up to 1600 K. The model predictions are compared with the results of alternative DFT-based approaches to free-energy modeling as well as with experimental data.