August 2013 - Allocations-admins - mailman3.cels.anl.gov

New LCRC report submitted for Chaos
by support＠lcrc.anl.gov 26 Aug '13

26 Aug '13

Full project report at https://accounts.lcrc.anl.gov/reporting/project/2013/?project=Chaos

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[LCRC Accounts] Yearly Allocation Request from LiBattModeling
by accounts＠lcrc.anl.gov 26 Aug '13

26 Aug '13

Hello, A yearly allocation for the LCRC cluster has been requested with the following updated information: Submitter/PI: Roy Benedek Project Name: LiBattModeling Division: CSE Project title: Lithium-Ion Battery Electrode Modeling Associated funding: Advanced Battery Research Program, Office of Vehicle Technologies, U. S. Department of Energy Other Systems: NERSC (about 100K core hrs.) Science: First principles local-density-functional-theory methods are applied to calculate physical and electrochemical properties of lithium-ion-battery-electrode materials. This work complements an experimental program in the Battery Department of CSE to characterize the degradation process known as voltage fade, and to find a solution for it. Project description: Composite materials with composition xLi2MnO3•(1-x)LiMO2, where M=mixtures of Mn, Co, Ni, etc., show high initial capacity, however, the voltage degrades with cycling, a severe drawback for commercial applications. Our modeling is directed at characterization of the atomic-scale instabilities that lead to voltage fade, and to identify compositions that inhibit the fade. Our previous work has suggested that Mn is unstable with respect to migration from octahedral to tetrahedral sites in the presence of oxygen vacancies that are created during the first charge. Our strategy is to replace the Mn in the Li2MnO3 component of the material with a late transition metal that has a stable pentavalent oxidation state in an octahedral environment, which would help stabilize against oxygen loss during the first charge. An ideal candidate M’ (to replace Mn) would be one that (a) forms a composite xLi2M’O3•(1-x)LiMO2 in which the majority of M’ resides in L i2M’O3 domains; (b) is stable with respect to migration to tetrahedral sites in the Li2-xM’O3 structure in both 4+ and 5+ states; and (c) M’ ions dissolved in the LiMO2 component of the structure would be stable with respect to migration from octahedral to tetrahedral sites in the delithiated state. The candidate M’ elements include V, Cr, Fe, Mo, Ru. Project URL: Current FY Hours Used: undetermined amount New FY Requested allocation: 400000 Q1: 100000 Q2: 100000 Q3: 100000 Q4: 100000 Justification: Thank You, The LCRC Accounts System

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New LCRC report submitted for DFT-defects-UO2
by support＠lcrc.anl.gov 23 Aug '13

23 Aug '13

Full project report at https://accounts.lcrc.anl.gov/reporting/project/2013/?project=DFT-defects-U…

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New LCRC report submitted for DFT-defects-UO2
by support＠lcrc.anl.gov 23 Aug '13

23 Aug '13

Full project report at https://accounts.lcrc.anl.gov/reporting/project/2013/?project=DFT-defects-U…

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[LCRC Accounts] Project Request: CeO2-voids-bubbles
by accounts＠lcrc.anl.gov 23 Aug '13

23 Aug '13

Hello, A new project on the LCRC cluster has been requested. Please forward the information on to the LCRC Allocation sub-committee. Applicant's name: Zhigang Mei Applicant's institution: ANL Applicant's division: NE Project Name: CeO2-voids-bubbles Project title: Void and Gas Bubble Formation in Doped Ceria: Role of Oxygen Defects and Fission Gases Diffusion Associated funding: LDRD Other Systems: CNM-Carbon, LCRC-fusion Science: Cerium dioxide (CeO2) is an important material with a wide range of technological applications. It is used as an electrolyte in solid oxide fuel cells (SOFCs), as a catalytic converter in the automotive industry or as a model material for PuO2 in nuclear energy applications. It has a fluorite structure (space group Fm3m [1]) and can develop a complex pattern of defects, depending on temperature and oxygen pressure [2]. Its extended hypo-stoichiometric domain was experimentally confirmed by Bevan and Kordis [3]. A review of oxygen diffusion in oxides, including surface and grain boundary effects, is available in Mayer et al. [4]. Dieckmann [5] published a detailed presentation of the basic concepts related to point defects and transport in non-stoichiometric oxides, including ceria. Considerable effort was devoted to improving the oxygen ion conductivity in ceria by optimizing the doping elements and concentrations. In the case of mixed oxide (MOX) nu clear fuels (UO2+x, PuO2-x), the point defects that survive the initial damage due to irradiation form extended defects, such as vacancy clusters, dislocation loops and voids. These nano-scaled defects impact the microstructure of the fuel, leading to degradation of its thermal and mechanical properties. In order to fully understand and to be able to accurately predict the microstructural evolution under irradiation, elucidating the underlying formation mechanisms of the extended defects is very important. The current goal of studying CeO2 is to understand the formation and evolution of nano-scaled defects in irradiated oxide nuclear fuels, including vacancy clusters, lattice voids, dislocation loops, and gas bubbles. There is essentially a multi-scaled problem, since the size of these defects covers a wide range length scale, from a few Angstroms to a few hundred of nanometers. Meanwhile, the formation of defects evolves diffusion of point defects over a long period of time, typically in the nanosecond-microsecond regime. A number of ion beam implantation experiments on CeO2 have been conducted with common fission gas species: Kr and Xe [6, 7]. Under different ion irradiation conditions, such as irradiation temperature, ion dose and energy, dislocation loops, voids and gas bubbles form at different stages. However, the formation and growth of these defects are still unclear. For example, completely different void size distributions, with void diameter from 0.5m to 5nm, were ob served for 1MeV Kr irradiated 5% La doped CeO2 and 25% La doped CeO2 at 600 °C [6]. Defects and their diffusion in CeO2 are essential to understand this observation. Critical questions relevant to the formation of void and bubble in irradiated CeO2 include: 1) what is the driving force for Xe and other fission gas to form clusters; 2) how does the size affect the stabilities of lattice voids and gas bubble; 3) how does Xe and vacancy diffusivities relate to the diffusivity of Xe clusters. Additionally, the formation and growth of dislocation loops in CeO2 was found to be strongly affected by temperature and non-stoichiometry. Due to the limitation of current experimental technique, it is difficult to track the position of oxygen atom and investigate the nucleation of dislocation loop from atomistic scale using in-situ TEM. So far the microscopic understanding of the formation of dislocation loop under irradiation is still not clear. The formation mechanism for these nano-sc aled defects are of critical importance to understand and further improve the irradiation tolerance of nuclear fuel materials and can only be answered by using appropriate computer simulation techniques to analyze and enhance the experimental information. The purpose of this study is to provide a united view of the effect of non-stoichiometry and temperature on the formation and evolution of nano-scaled defects, i.e., defect clusters, voids and fission gas bubbles, in irradiated ceria using existing experimental data, multiscale modeling and computer simulations. Project description: We will use DFT to calculate the formation of point defects and clusters. The effect of temperature and oxygen pressure on the stabilities of defects will be explored. We will use nudged elastic band (NEB) method to investigate the migration barrier of point defect, defect clusters and fission gas in doped ceria. The predicted barrier will be used in a kMC framework to study the long-time oxygen and fission gas diffusivities. In parallel to DFT calculations, we will explore point-defect clustering and formation of voids and gas bubbles in ceria using accelerated molecular dynamics technique, such as metadynamics. The formation of defect clusters evolves diffusion of point defects over a long period of time, typically in the nanosecond-microsecond regime. These accelerated molecular dynamics method will been used to link the MD-observed defect configurations with the experimentally accessible radiation-induced extended defects. Due to the strongly correlated nature of the f electrons, more accurate methods, such as the LDA+U and hybrid density functional methods are required to overcome the limitations of conventional DFT method. These new methods require one order of magnitude longer computational time. Highly efficient DFT codes, such as VASP, will be utilized for DFT calculations. To go beyond point defects, we will use highly parallel MD code LAMMPS to study the formation and migration of defect clusters, voids and gas bubbles in realistic time scale, nanosecond-microsecond regime. These simulations need significant amount of computational time. We will employ DFT calculations to study the formation energies and stabilities of point defects and point defect clusters in non-stoichiometric and rare-earth doped ceria using a 3×3×3 unit cell of ceria with around 300 atoms. These defect formation energies will be used to estimate the defect concentrations based on point defect model. The most computationally intensive calculations are focused on the study of oxygen defects, defect clusters and fission gas diffusion in rare-earth doped ceria. We will explore the several effects on the migration energy in doped ceria: 1) role of doping elements, 2) doping concentration, 3) type of point defects, 4) morphology of defect clusters; 5) cation ordering around diffusion atoms; and 6) role of fission gas. We expect the computational requirement for the proposed study to be substantial. For a typical DFT-NEB calculation of oxygen diffusion barrier in ceria using a supercell with ~100 atoms, it requires ~1000 core hours for a five -image NEB calculations. By considering all the six effects on the diffusion, we will calculate ~150 coverage-dependent diffusion barriers. Thus we estimate ~150,000 core hours are needed for all the DFT calculations. With predicted migration barriers, a parallel kinetic Monte Carlo code SPPARKS will be adopted to study the long-time oxygen and fission gas diffusivities in doped ceria. The diffusivity of oxygen and fission gas will be investigated with respect to doping concentration and temperature. A total of ~500 coverage-dependent diffusivity calculations are required. The simulation system will be based on a 20×20×20 unit cell of ceria to cover all the doping concentration we are interested. Our test shows that a minimum 500,000 KMC steps are required to achieve good convergence for diffusivities, requiring ~100 core hours for each diffusivity calculation. Therefore we estimate ~50,000 core hours are needed for the KMC calculations. On the other hand, MD simulations with several initial fission gas concentrations, temperatures, and gas pressures will be used to explore on the nucleation of voids and gas bubbles in pure ceria. A relative large cell size is critical for simulating voids and gas bubbles. A computational cell with 200,000-500,000 atoms is required for setting up the pressure in the system. The most common simulation time in this study (10 ns) requires up to 20 million simulation time steps that will be performed for several gas concentrations, temperatures and gas pressure. To cover all the effects, it requires ~12 coverage-dependent MD simulations. Our benchmark calculations show that ~20,000 cores hours are needed for one typical MD run. We estimate ~250,000 core hours are needed for all the MD calculations. The total amount of CPU time needed to finish all the DFT, KMC and MD calculations for this project will be approximately 450,000 core hours. We expected three people will involve in this project. Project URL: Requested allocation: 440000 Q1: 110000 Q2: 110000 Q3: 110000 Q4: 110000 Justification: The requester has used undetermined amount hours of their initial startup project. In addition to approving an initial amount, please specify a Category and Subcategory for this project. For a list of the current selection of approved categories, please see: https://wiki.lcrc.anl.gov/wiki/Processes/Categories Once the Allocation committee has approved the project, please go to the Project Management page to create it: https://accounts.lcrc.anl.gov/projects.php Thank You, The LCRC Accounts System

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[LCRC Accounts] Yearly Allocation Request from SnI4
by accounts＠lcrc.anl.gov 22 Aug '13

22 Aug '13

Hello, A yearly allocation for the LCRC cluster has been requested with the following updated information: Submitter/PI: Michael Hu Project Name: SnI4 Division: XSD Project title: Crystalline and amorphous structures of SnI4 Associated funding: DOE and NSERC (Canada) Other Systems: Science: Molecular solid SnI4, when put under pressure, demonstrates rich structure transformations, and complex processes of polymerization, metallization, and amorphization. Adding to Mossbauer spectroscopic and x-ray diffraction studies, we recently conducted phonon spectrum measurements of SnI4 under pressure. In this proposal, we outline our research forward with material simulation using modern algorithms and supercomputers, which we believe is critical to interpret our experimental results and gain insights to material properties under extreme conditions. Project description: Tin iodide SnI4 is a van der Waals-bonded molecular solid with a face-center cubic structure (fcc) under ambient conditions. It is well established that under compression at room temperature to 15 GPa a reversible solid-state amorphization was found (S. Sugai, J. Phys. C 18, 799 (1985). using x-ray diffraction and Raman scattering. Later it was found that the amorphization was not originated directly from the cubic phase (phase-I) but through an intermediate crystalline metallic phase II stable above 7.2 GPa (N. Hamaya, K. Sato, K. Usui-Watanabe, K. Fuchizaki, Y. Fujii, and Y. Ohishi, Phys. Rev. Lett. 79, 4597 (1997). The precise structure of phase-II has not yet been clarified. The amorphous structure was found to crystallize to a fcc-like lattice at 61 GPa. Several theories have been proposed to account for the loss crystallinity in the diffraction pattern and, perhaps, the idea of pseudomelting (S. Sharma and S. Sikka, Prog. Mater. Sci. 40, (1996) is the most interesting. Recently, density of the vibrational states as a function of pressure were measured using nuclear inelastic x-ray scattering experiments to explore the mechanism of the amorphization. The theoretical study proposed below is aimed to elucidate all the experimental results obtained so as to uncover the mechanism for the amorphization process. We believe is critical to interpret our experimental results and gain insights to material properties under extreme conditions. The outline of the research is as follow. The stability of the lattice in the ambient structure will be examined using finite temperature self-consistent lattice dynamics and molecular dynamics calculations. The purpose is to investigate the role of (soft) phonons in the crystal -> crystal transition at ca. 7.2 GPa. Using evolution method, possible candidate structures will be predicted and their properties (i.e. structural and electrical) will be compared with experiment. Constant molecular dynamics calculations will then be performed on prospective phase II structures to examine the mechanism of amorphization. The final goal is to characterize the crystalline structure observed experimentally at 61 GPa. First-principles methods static and dynamic calculations based on density functional approximation will be performed. Specially, structural prediction using evolution algorithms (C. Glass and A. Oganov, J. Chem. Phys. 124, 244704 (2006); Y. Wang, J. Lv, L. Zhu and Y. Ma, Phys. Rev. B 82, 094116 (2010)) and constant pressure molecular dynamics calculations will be performed. The ambient fcc unit cell of SnI4 is consisted of 40 atoms. Any calculations using a supercell model will require exceeding 320 atoms. For this purpose, significant computational resource is required. The density functional codes to be used in this study are well maintained and proven highly-parallel public domain programs SIESTA and VASP. Both codes can be used for static and dynamic calcu lations. Structural search will be performed using our own implementation of the evolution algorithm (Y. Yao, J.S. Tse and K. Tanaka, Phys. Rev. B 77, 052103 (2008)). Structural search and molecular dynamics calculations are computationally (both on the speed of the CPU and memory capacity) very demanding. In the initial stage, an estimate of the computation requirement is about 400,000 CPU-hours on the IBM peta computer cluster. Project URL: Current FY Hours Used: undetermined amount New FY Requested allocation: 360000 Q1: 80000 Q2: 80000 Q3: 100000 Q4: 100000 Justification: Thank You, The LCRC Accounts System

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New LCRC report submitted for Cat_Biomass
by support＠lcrc.anl.gov 22 Aug '13

22 Aug '13

Full project report at https://accounts.lcrc.anl.gov/reporting/project/2013/?project=Cat_Biomass

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New LCRC report submitted for Cat_Biomass
by support＠lcrc.anl.gov 22 Aug '13

22 Aug '13

Full project report at https://accounts.lcrc.anl.gov/reporting/project/2013/?project=Cat_Biomass

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[LCRC Accounts] Yearly Allocation Request from NuclearStructure
by accounts＠lcrc.anl.gov 22 Aug '13

22 Aug '13

Hello, A yearly allocation for the LCRC cluster has been requested with the following updated information: Submitter/PI: Richard Chasman Project Name: NuclearStructure Division: PHY Project title: Optimization of many-body wavefunctions Associated funding: DOE/Office of Nuclear Physics Other Systems: desktop Science: The purpose of this work is to obtain a good description of low-lying nuclear states, going beyond a mean-field description. It becomes necessary to go beyond the mean-field approximation when the nucleus of interest is transitional in some sense, e.g. transitional between a spherical shape and a deformed shape. The need to go beyond a mean-field description is particularly important for excited states. Project description: We are studying medium mass nuclei using an interaction that includes n-p pairing together with deformation. At present, we are investigating several interactions that give rise to deformation in order to determine which ones provide a good description of nuclei having almost equal numbers of protons and neutrons. We are generalizing the treatment to rotationally invariant interactions. Project URL: Current FY Hours Used: undetermined amount New FY Requested allocation: 4000 Q1: 1000 Q2: 1000 Q3: 1000 Q4: 1000 Justification: Thank You, The LCRC Accounts System

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New LCRC report submitted for Comp_Nanocatalysis
by support＠lcrc.anl.gov 21 Aug '13

21 Aug '13

Full project report at https://accounts.lcrc.anl.gov/reporting/project/2013/?project=Comp_Nanocata…

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