From a recent DFT calculations [10], it is found that the predominant low energy surfaces of LMO are (100), (110) and (111) facets. Therefore these surfaces appear to be a logical modeled system to start with. To address the problems that related to our experimental colleagues findings, the simulation of Mn dissolvation, dissolution and diffusion into electrolyte interfaces will be performed with and without the explicit solvent in the simulation. Subsequently the effect of external bias voltage (i.e. the external uniform electric field) on the LMO solid /organic solvent interface will be investigated using VASP code.
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: Kah Chun Lau Applicant's institution: ANL Applicant's division: MSD, CLS-LCRC Project Name: Electric_Interface Project title: Electrified Interfaces from First-Principle Studies Associated funding: DOE BES-CEES EFRC, DOE BES-JCESR Other Systems: Science: Electrified Interface of solid and solid/liquid electrolytes in electrochemical system is presently the subject of great interest to electric energy storage research at Argonne (i.e. BES-JCESR, BES-CEES-EFRC), and also among the scientific community. Within this wide area of research problems, the effect of external bias voltage on the interface at the atomistic scale is the basis of our fundamental understanding, design and application in this field. To include the external bias voltage in atomistic simulation based on first-principle study (DFT), the theoretical treatment with the application of a finite homogeneous electric field proposed by Nunes et. al. [1] is a reasonable and practical method based on DFT calculations. Within this proposal, the key parts of the proposed study will consists of three independent yet related topics: (I) the electrified interface of organic electrolyte/oxide, (II) electrified interface of water/metal, and (III) electrified oxide solid. For the case study of electrified interface of oxide/organic electrolyte, the well-known problem of solid-phase instability at external electric potential that exemplified by metal dissolution from manganese (Mn)-based oxide cathode surface that found in next generation Li-ion battery system [2] will be addressed. To go in parallel with our experimental colleagues, the modeled system will based on the spinel LiMn2O4 (LMO)/ GenII electrolyte (i.e. 1.0 LiPF6 in ethylene carbonate: ethyl methyl carbonate electrolyte with 3:7 ratio by weight) developed at ANL. For this system, the DFT atomistic simulation of Mn dissolution at anode interface has been performed by one of the PIs (K.C. Lau, MSD) [3]. In present proposal, the primary focus will be Mn desolvation, dissolution and diffusion at the cathode interface will be investigated. To simplify the model, the Ab Initio Molecular Dynamics (AIMD) simulation of LMO/electrolyte interface will be only based on the lowest energy LMO facet that yet to be determined. In addition, the effects of external electric field on this system (e.g. diffusion, desolvation, electronic properties, etc.) will also be investigated. The microscopic structure of the water/metal interface is still controversial and an active area of research. We propose to employ methods developed Sprik, Siepmann, Izekov and Voth [4,5,6] to generate realistic models of the bilayer of water on a metal surface. This approach employs molecular dynamics with a force-field that includes polarization to model the image dipole in the metal to determine an initial geometry for ab initio molecular dynamics to model reactions. The pre-equilibration by molecular dynamics allows the long range structure of the aqueous phase to equilibrate with field generated by the image dipole in the metal and the applied potential. The electronic structure calculations will exploit the Effective Screening Method implemented in OpenMX by Ohwaki, et al. [7] to model reactions on the metal/water interface under an applied electrical bias. This model will used 2D periodic boundary conditions and a semi-infinite effective medium to model the solven t outside slabs of water above slab of Pt. The slab of water will be 3 nm thick to include the water bilayer and a dozen layers of water to model the aqueous phase. Without the interface, the study of the effect of external electric field on a solid that present in electrochemical synthesis route is also an interesting yet not well been addressed. In this proposal, we will focus on lithium superoxide crystal that recently electrochemical been synthesized for the first time at ANL. From one of PIs’ (K.C. Lau, MSD) previous study [8,9], it has been shown that this oxide is semi-metallic ferromagnetic system originated from its open-shell 2p electrons of O2- molecules in crystal lattice. However the basic understanding of this system has been limited to weakly-correlated electronic structure description based on conventional DFT calculations that cannot accurately predict the ferromagnetic order of the correlated oxygen p-electrons in lithium superoxide. To resolve this issue, a systematic study of Quantum Monte Carlo (QMC) calculations of the magnetic and electronic states of this system will be carried out. From the proposed QMC calc ulations, the important U-values for the Hubbard-corrected DFT (DFT+U) will be determined. Project description: The project can be divided into three related problems: 1) Electrified Interfaces of spinel LMO 2) Electrified Water/Pt Interface The oxygen reduction reaction will be modeled on Pt(111) to evaluate the utility of OpenMX. This model will used 2D periodic boundary conditions and a seminfinite effective medium to model the solvent outside slabs of water above 1nm slab of Pt. The slab of water will be 3 nm thick to include the water bilayer and several layers of water to model the aqueous phase. We will model this reaction with and without an applied voltage. The initial model involve a hundred molecules of water and hundred atoms of Pt in a 10Å x 10Å x 40Å box, and the thermal equilibrated configuration will obtained based on classical MD atomic trajectory using LAMMPS code. 3) QMC validated DFT-U of Lithium Superoxide Magnetism Based on the DFT obtained lowest energy crystalline structure [8], the high-level QMC calculation of lithium superoxide crystal will be used to investigate the ferromagnetism and electronic properties of this system. Based on QMC data, the U-value that needs to compute Hubbard DFT-U calculations will be determined. In addition, the intrinsic spin-orbit effect and external electric-field on its electronic properties will be addressed. Calculation size: The smallest cells for which the effects of interest can realistically be simulated for LMO/electrolyte AIMD simulation will contain about five hundred atoms, with perhaps a 200 atom slab of LMO, and 300 atoms of electrolyte. All numerical shortcuts (gamma-point only, soft pseudopotentials) will be exploited. We expect to run on 256 processors. Of the calculations proposed here, the AIMD simulations (item 1) will have the largest CPU-time requirements per unit MD-time step of 1 fs. The AIMD simulations performed in NVT-ensemble simulations may require about 1 processor-hr per time step, for a cell size of about 500 atoms (using perhaps 256 processors). Obtaining a reasonably good MD statistics calculation may require of the order of 200 k processor hrs. Simulations of the 2D periodic water/Pt metal system (item 2) are expected to require of order 1 processor-minute per relaxation step or MD step. Considering three different interfaces sampling at a given temperature, and of order 2x10**5 steps for each case, the total time for this step would also be of order 100k processor hrs. Thus a 300k processor hrs is needed. For item 3 calculations, the most expensive calculation is QMC simulation that cost about ~ 100k processor hrs. For DFT+U calculations, about 100k processor hrs will be needed. Thus, requirements for the entire project are thought to be of order 700,000 processor hours. Industry partnership: Project URL: Requested allocation: 700000 Q1: 150000 Q2: 200000 Q3: 200000 Q4: 150000 Justification: VASP is well known to have scalability issues. Although it is very efficient code for models contains 100s of atoms, the parallel scalability for systems of this size is only 100s of cores. Although better parallel scalability can be obtained for larger models, the size scalablity becomes a major issue as O(N3) terms become a bottleneck in the simulation. The scalability of Abinit and Quantum Espresso is similar to that of VASP. OpenMX is an O(N) code with good parallel scalability. A recent publication by Duy and Osaki [11] has demonstrated the excellent parallel scalability of OpenMX to over a 100K cores on the K computer. Quantum Monte Carlo (QMC) codes are known to have good parallel scalability with poor size scalability. For example, Wagner et al. [12] demonstrated good parallel scalability of QWALK to 4 thousands cores of the Franklin supercomputer at NSERC. QMC will provide reference energies, which include all electronic correlation for comparison to the results of density functional approximations and determination of the U in DFT+U. LAMMPS is well known to have good parallel scalability References: 1. R. W. Nunes and X. Gonze, Phys. Rev. B 63, 155107 (2001). 2. C. Zhan, J. Lu, A.J. Kropf, T. Wu, A.N. Jansen, Y. Sun, X. Qiu, K. Amine, Nature Comms. 4, 3437 (2013) 3. K.C. Lau, J. Lu, L.A. Curtiss, K. Amine (in preparation). 4. J. I. Siepmann, M. Sprik, J. Chem. Phys. 102, 511 (1995). 5. S. Izvekov, G. A. Voth, J. Chem. Phys. 115, 7196 (2001). 6. J. Carrasco, A. Hodgson, A. Michaelides, Nature Mater. 11, 667 (2012). 7. T. Ohwaki, M. Otani, T. Ikeshoji, T. Ozaki, J. Chem. Phys. 136, 134101 (2012). 8. K.C. Lau, J. Greeley, L.A. Curtiss, J. Phys. Chem. C 115, 47, 23625 (2011). 9. J. Lu et. al. (submitted). 10. A. Karim, S. Fosse, K. A. Persson, Phys. Rev. B 87, 075322 (2013). 11. T.V.T. Duy, T. Osaki, Comp. Phys. Comm. 185, 777 (2014). 12. L.K. Wagner, M. Bajdich, L. Mitas, J. Comp. Phys. 228, 3390 (2009). Storage requirements: 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