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: Sridhar Sadasivam Applicant's institution: ANL Applicant's division: NST Project Name: perovskite_scat Project title: Electron-phonon and phonon-phonon scattering in lead halide perovskites Associated funding: Department of Energy (LDRD) Other Systems: Carbon cluster, Center for Nanoscale Materials Science: In this proposal, we seek to understand the energy cascade mechanisms between electrons, optical and acoustic phonons in methylammonium lead halide (MAPbI3) perovskites. Organic-inorganic halide perovskite materials are promising candidates for third-generation photovoltaics. Perovskite solar cells are manufactured using inexpensive solution-based techniques [1], and their energy conversion efficiency has increased from 3.8% in 2009 to 19% presently [2], with enormous potential for further improvements. One of many remarkable properties of these materials is the slow relaxation of high-energy charge carriers that could allow their use in highly efficient hot carrier solar cells [3]. However, intuition regarding the dynamics of energy cascade processes in perovskite materials is still lacking, and predictive first-principles calculations of the scattering strength between energy carriers are scarce. In this proposal, we seek to perform first-principles calculations under the density functional theory (DFT) framework to predict electron-phonon and phonon-phonon scattering times in methyl ammonium lead iodide perovskites. Electron-phonon scattering calculations will be performed under the framework of density functional perturbation theory (DFPT) with a Wannier interpolation of electron-phonon matrix elements to dense electron and phonon wavevector grids [4-6]. Phonon-phonon scattering calculations will be performed using a real-space supercell approach where finite differences of forces due to atomic displacements will be used to obtain the third-order interatomic force constants [7]. The proposed work is expected to provide a fundamental understanding of energy transfer processes between electrons and phonons in halide perovskite materials, and also provide insights that could guide experimentalists to engineer materials for hot-carrier solar cell applications. References: 1. M.M. Lee, J. Teuscher, T. Miyasaka, T.N. Murakami, H.J. Snaith, Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites, Science, 338, 643-647, 2012 2. H. Zhou, Q. Chen, G. Li, S. Luo, T. Song, H. Duan, Z. Hong, J. You, Y. Liu & Y. Yang, Interface engineering of highly efficient perovskite solar cells, Science, 345, 542-546, 2014 3. Y. Yang, D.P. Ostrowski, R.M. France, K. Zhu, J. van de Lagemaat, J.M. Luther & M.C. Beard, Observation of a hot-phonon bottleneck in lead-iodide perovskites, Nature Photonics, 10, 53-59, 2015 4. M. Bernardi, D. Vigil-Fowler, C.S. Ong, J.B. Neaton & S.G. Louie, Ab Initio Study of Hot Electrons in GaAs, Proceedings of the National Academy of Sciences, 112, 5291-5296, 2015 5. F. Giustino, M.L. Cohen & S.G. Louie, Electron-phonon interactions using Wannier functions, Physical Review B, 76, 165108, 2007 6. J. Noffsinger, F. Giustino, B.D. Malone, C-H. Park, S.G. Louie & M.L. Cohen, EPW: A program for calculating the electron-phonon coupling using maximally localized Wannier functions, Computer Physics Communications, 181, 2140-2148, 2010 7. A. Togo, L. Chaput & I. Tanaka, Distribution of phonon lifetimes in Brillouin zones, Physical Review B, 91, 094306, 2015 Project description: The proposed work involves two primary tasks as outlined below. Both these calculations will involve use of the planewave DFT code Quantum Espresso with fully relativistic pseudopotentials for Pb and I atoms. The inclusion of spin-orbit coupling requires the use of large memory nodes and the 64 GB nodes on the Blues cluster are expected to be ideal for such calculations. 1. Computation of electron-phonon scattering rates: The first step in the calculation of electron-phonon scattering is the computation of phonon bandstructure along with the variation in self-consistent potential with respect to atomic displacements. Both these calculations will be performed under the framework of DFPT and is already implemented within the phonon module of Quantum Espresso. All DFT calculations would also involve spin-orbit coupling, since relativistic effects are important to consider for the heavy Pb and I atoms. Considering a 12 atom cubic unit cell of MAPbI3, the number of DFPT calculations required for a 4x4x4 phonon wavector grid is 36. Preliminary tests on the Blues cluster indicate that dynamical matrix calculations at a single phonon wavevector on 1 node (16 cores) takes approximately 150 hours. Hence, a full phonon dispersion calculation over 36 wavevectors will require a total time of approximately 36 x 16 x 150 = 86,400 hours. The second part of the computations will involve the use of Electron-Phonon Wannier (EPW) code to interpolate electron-phonon matrix elements from the coarse grid used in DFPT calculations to dense grids needed for convergence of electron and phonon self-energies. EPW calculations will need to be parallelized using the same number of processors used in the computation of phonon dispersion. The time needed for Wannier interpolation scales linearly with the number of grid points at which the electron-phonon matrix elements need to be obtained. Assuming that four calculations on different grid densities will be needed for studying the convergence of electron-phonon scattering rates, a total time of about 20,000 hours is expected to be sufficient for calculation of electron and phonon scattering self-energies. 2. Computation of phonon-phonon scattering rates Unlike the electron-phonon scattering rates that were obtained using DFPT, the phonon-phonon scattering rates will be computed using a real-space supercell approach. Assuming a 2 x 2 x 2 supercell of 96 atoms, along with a 5 Angstrom cutoff distance for third-order force constants, the number of supercell DFT calculations needed is approximately 5200 (after considering symmetries of the crystal structure). Preliminary tests on the Blues cluster indicate that each supercell calculation requires about two hours on 2 nodes (32 cores). Hence the computation of phonon-phonon scattering rates is expected to require about 5200 x 32 x 2 = 332800 hours. The estimated time required for the various aspects of the project are summarized below: 1) DFPT calculations of phonon dispersion: 86400 core hours 2) EPW calculation of electron-phonon scattering rates: 20000 core hours 3) Phonon-phonon scattering rate calculations using real-space supercell approach: 332800 core hours The total requested time is 440,000 core-hours. Dr. Sridhar Sadasivam and Dr. Pierre Darancet will be responsible for carrying out the simulations. Industry partnership: Project URL: Requested allocation: 440000 Q1: 100000 Q2: 150000 Q3: 100000 Q4: 90000 Justification: 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