Is there a future for quantum chemistry on supercomputers? Jürg Hutter Physical-Chemistry Institute, University of Zurich Chemistry Chemistry is the science of atomic matter, especially its chemical reactions, but also including its properties, structure, composition, behavior, and changes as they relate the chemical reactions.(Wikipedia) Chemistry is the science that invents what it studies. Theoretical Chemistry Theoretical chemistry is the study of chemistry via fundamental theoretical reasoning, usually within physics and mathematics. i h ˙ ψ = H ψ Quantum Mechanics S = k log W Statistical Mechanics Computational Chemistry Computational chemistry is a branch of chemistry that uses principles of computer science to assist in solving chemical problems. Quantum Mechanics Molelcular Orbital Theory Density Functional Theory Ab Initio Calculations Statistical Mechanics Molecular Dynamics Monte Carlo Transition State Theory Quantum Chemistry & Transition State Theory Construct potential energy surface for a few degrees of freedom or find a few stationary points. Quantum Chemistry Software • Well tested and robust programs • User friendly and well documented • Gaussian • GAMESS • Turbomol • Molpro • ORCA, ADF, MOLCAS, Success of Quantum Chemistry Quantum Chemistry Software DFT Development of the usage of computational quantum chemistry, as measured by two different metrics. The top curve gives the number of citations to software packages per year, while the lower curves provide the number of citations of particular electronic structure methods (specifically pure and hybrid density functionals). Data are from the Web Science (courtesy of Emilio Artacho). Quantum Chemistry on Supercomputers Quantum Chemistry on Supercomputers NIC Jülich (Germany) 5 % CSC (Finland) 10 % Oak Ridge National Lab (US) 17 % CSCS (Switzerland) 16 % Quantum Chemistry on Supercomputers • Most standard applications fit on mid-range computers Cloud/Grid Computing • Larger systems → condensed phase → configurational sampling New Approaches for New Problems [...]... transfer dynamics Summary • Computational Quantum Chemistry is still a rapidly growing field • Standard applications are done by "non-experts" on small and mid-range computers • Applications on High-Performance Computer is now dominated by • Complex systems (condensed phase) with strong overlap to material science and bio-sciences • ab initio molecular dynamics for statistical sampling ...Ab Initio Molecular Dynamics R Car and M Parrinello, Phys Rev Lett 55 2471 (1985) Electronic Structure Calculations + Molecular Dynamics Ab Initio Molecular Dynamics System Size AIMD 10-100 Atoms 10-100 100-1000 Atoms Standard QC Number of Calculations 10’000 - 1’000’000 Supercomputers are needed SIESTA, Quantum- Espresso, CPMD, CP2K AIMD Scales on Supercomputers History of the performance of AIMD... computer platforms (Francois Gygi, UC Davis) AIMD: Example Application Dye-Sensitized Solar Cells (DSSC) 1 1 Wikipedia Grätzel Cell Projects • Dynamics and structure of solvent (acetonitrile) at semiconductor (TiO2) interface F Schiffmann et al., J Phys-Cond Mat 20 064206 (2008) • Distribution of electrolyte (I− , I− ) at the interface 3 F Schiffmann et al., PNAS 107 4830 (2010) • Regeneration mechanism... reaction of I− in solution necessary 2 Experiment finds only very small concentrations of I− in 2 solution Postulated Regeneration Mechanism Summary • Complex systems/interfaces can be studied with AIMD • Most complex model of a DSSC studied had 1751 atoms • Insight in various process of DSSC has been gained • Ion distribution at interface • Regeneration mechanism • Electron transfer dynamics Summary... distribution • First layer of ACN passivates the surface (no direct contact of TiO2 to electrolyte) • I− concentration peaks at 10 Å from surface (all other ions studied have decreasing concentrations near the interface) I− /I− Association (Free Energy) 2 I− /I− Association 2 • Barrierless association of I− /I− with dye molecules 2 • I− from interaction of dye/I2 complex with I− 3 • No bimolecular... MD simulation using PBE (DFT+U) • CPU time on 1024 cores Cray-XT5 • SCF iteration: 13.7 seconds • MD time step: 164 seconds DSSC: Complex Electronic Structure Relative position of orbital levels important for charge localization and for electron injection dynamics I− Distribution at Interface I− Distribution at Interface • Solvent near interface cannot be described by single dielectric constant • Non-monotonic... dye at interface F Schiffmann et al., PNAS 107 4830 (2010) • Binding and IR spectra of dye (N3) on TiO2 surface F Schiffmann et al., J Phys Chem C 114 8398 (2010) • Electron transfer dynamics (dye → semiconductor) F Schiffmann, Thesis UZH 2010 Computational Model • Almost complete model of a DSSC • 1751 atom computational cell, 864 (TiO2), 60 dye+electrolyte, 828 solvent • 9346 electrons, 22951 basis . studies. Theoretical Chemistry Theoretical chemistry is the study of chemistry via fundamental theoretical reasoning, usually within physics and mathematics. i h ˙ ψ = H ψ Quantum Mechanics S = k log W Statistical. Statistical Mechanics Computational Chemistry Computational chemistry is a branch of chemistry that uses principles of computer science to assist in solving chemical problems. Quantum Mechanics. Molelcular Orbital Theory Density Functional Theory Ab Initio Calculations Statistical Mechanics Molecular Dynamics Monte Carlo Transition State Theory Quantum Chemistry & Transition State Theory Construct