Hello, A change in allocation has been requested: Requester: liali (Liang Li) Project: Cat_LIO Title: First-Principles Investigations of the Delithiation Mechanisms and Surface Stabilities of Li-rich, Ir Oxide-Based Cathode Materials Description: The structure and energetics calculations of Li2IrO3 and Li8IrO6 will be performed using the plane wave DFT code VASP, with supplied projector augmented wave (PAW) atomic potentials and Perdew-Becke-Ernzerhof (PBE) exchange-correlation functionals. On-site coulomb interactionis accounted for by Hubbard U correction. Dispersion interaction may play an important role in layered Li2IrO3, so several types of optimized functionals that incorporate nonlocal dispersion corrections will be tested and compared with experimental X-ray diffraction (XRD) data to ensure that our calculations yield reasonable geometric properties. XANES spectra simulation will be carried out using OCEAN code5 that utilizes a GW and Bethe-Salpeter equation (BSE) formalism. The following calculations are specifically proposed in this study, and detailed accounting of the computational time requested for each calculation is also presented: Structural variation and electronic properties of Li2IrO3 and Li8IrO6 during Li extraction will first be examined exhaustively, and the DFT energies obtained in this process will be used to determine the most stable configuration at various Li concentration. Bader charge analysis of transition metals and oxygen atoms will also be performed to understand the charge compensation mechanism. The Li atoms will be removed from the material in a sequential manner, i.e. the most energetically favorable structure at a particular Li concentration is used as the starting configuration in the following Li removal step. Li2IrO3 supercell contains 16 Li and 24 O atoms, whereas Li8IrO6 supercell contains 24 Li and 18 O atoms, so to sample the energies along the complete delithiation paths, taking into account of the structural symmetry, 136 and 200 calculations are needed for Li2IrO3 and Li8IrO6, respectively. In addition, to evaluate the possibility of oxygen loss at various Li concentrati ons, the oxygen vacancy formation energy will also be calculated at each of the Li concentrations, which results in 24×16+18×24=816 calculations. Each of the abovementioned structural relaxations requires approximately 8 hours on 32 cores, therefore, all together we expect to need (136+200+816)×32×8~295,000 core hours. The thermodynamic stabilities of low-index surfaces with all possible terminations will be examined, and the oxygen vacancy formation energies of each surface will also be calculate in order to understand the surface stability toward oxygen release. Due to the anisotropy of Li2IrO3 and Li8IrO6 structures, 7 types of surfaces need to be considered: 3 in {100} family of lattice planes, 3 in {110} and 1 in {111}. The complexity of atom arrangements lead to at least 2 possible terminations for each surface types. 10 atomic layers will be used to construct the surface slabs, and the structural relaxation needs roughly 12 hours on 96 cores. Thus, to obtain the energies of relaxed surface structures, 2×7×2×12×96~32,000 core hours are needed. After the favorable terminations of all 7 types of surfaces are identified, the oxygen vacancy formation energies at various local Li concentrations will be calculated. 5 different Li concentrations will be tested, which requires 2×7×5×12 ×96~80,000. Therefore, total core hours of ~112,000 will be a reasonable estimation. The XANES spectra of Li2IrO3 and Li8IrO6 with different Li and O vacancy concentrations will be simulated. Accurate treatment of the BSE formalism is computationally demanding and typically requires 15 hours on 96 cores for the systems under study. Considering there are 16 and 24 structures with various Li contents for Li2IrO3 and Li8IrO6, respectively, and 10 representative structures with O vacancies will also be calculated for Li2IrO3 and Li8IrO6, we therefore request (16+24+10+10)*15*96~86,000. The total time requested for this project is approximately 295,000+112,000+86,000~493,000 core hours. Current: undetermined amount Justification: Requested: 150000 A specific reason has been given: For the project entitled “First-Principles Investigations of the Delithiation Mechanisms and Surface Stabilities of Li-rich, Ir Oxide-Based Cathode Materials”, I was allocated with 209k core-hours in the first half of the fiscal year. My primary focus in the first few months was to identify all the thermodynamically stable phases of Li2-xIrO3 (0≤x<2) compounds based on density functional theory (DFT) calculations, as well as to simulate the X-ray Absorption Near Edge Spectra (XANES) using all the predicted lowest-energy structures. Two formalisms are adopted for determining the stable phases of Li2-xIrO3: 1) history-dependent Li removal and 2) complete screening of all possible structures based on electrostatic energy and subsequent calculations. The history-dependent Li removal formalism, as stated in the Project Description, requires 136 + 384 = 520 calculation, and each takes 7 hours on 24 cores. In total, this set of calculations consumes 520*7*24= 87,000 core-hours. The Li2IrO3 supercell for formalism 2) contains 8 Li atoms, thus there are 9 possible Li contents for Li2-xIrO3, with the two end compositions being Li2IrO3 (8 Li atoms) and IrO3 (0 Li atoms). We first ranked all the possible configurations at each Li content by their electrostatic energies, and then selected the 30 lowest-energy configurations for DFT calculations. There are 7x30=210 DFT calculations performed, and each of the calculations takes roughly 8 hours on 32 cores, therefore, 210*8*32=54,000 core-hours were used for structural calculations. After determining the stable structures, we then simulated XANES spectra for all the Li contents. These simulations are performed using OCEAN package, which utilizes a GW and Bethe-Salpeter equation (BSE) formalism and thus is computationally expensive. O K-edge XANES spectra for 8 structures with various Li contents are simulated, with each of them taking approximately 48 hours on 160 cores. Together the XANES simulation consumes 8*48*160=61,000 core-hours. The three sets of calculations above used in total 87,000 + 54,000 + 61,000 = 202,000 core-hours, which is roughly 96.6 % of the total amount I was allocated with for the first half of the year. Herein I request additional 150,000 core-hours for the second quarter of the year. This request is justified as follows: history-dependent Li removal will be performed on another Li irridate: Li8IrO6, and a total of 18×24+300 = 732 calculations are needed, with each of them taking 6 hours on 32 cores. All together this requires 732*6*32=141,000 core-hours. Another half of the originally requested core-hours (209k) will be used in the second half of the year, for surface structure calculations, as well XANES simulation of Li8-xIrO6. This needs to be approved and the final allocation amount decided upon. Thank You, The LCRC Accounts System