Computational methods for the exploration of potential energy surfaces with applications to nanoalloy materials.

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We develop high performance computational methods to explore potentialenergy surfaces (PES, mathematical functions that describe how the energy ofmolecules changes when the geometry of the molecule changes), thus providing thefoundation for studies of molecular structure and chemical reactivity. Successful implementationof this proposal will create a unique set of computational tools for studyingmolecular structures, transition states, and reaction paths,and for the simulation of systems with hundreds of atoms. These toolswill be of great importance to researchers in Canada and beyond.One of our methods mimics DFT and gives a computational speed-up of 4 to 6 orders of magnitude. It will allow the study of nanoalloyswith potential applications in catalysis and data storage devices.Taking clues from our recent discovery of bimetallic cages,we will search for new and bigger all-metal cages.Minima of the PES are equilibrium geometries of molecules; saddle points aretransition states; steepest descent lines connecting saddle points to minima are reaction paths;low energy regions in the vicinity of steepest-descent lines are importantfor detailed models of reaction mechanisms. We will continue to makeexpert use of quantum chemistry and density functional theory(DFT), combined with our own computer codes, to investigate PES. Students will get trained in research projects that combine method developmentand applications and will acquire a variety of skills: expertise in UNIXand quantum chemistry software, programming and shell scripting, mathematicalmodeling, and general scientific literacy. The projects are designed atvarious levels to address the needs and capabilities of undergraduate, postgraduate, and postdoctoral students.We will work on three fronts to study nanoalloys that have interestingproperties and potential use in catalysis and information technologies. (1) Global optimization. Evolutionary computing methods, like GeneticAlgorithms (GA), will be developed to determine the geometric structureof nanoalloy clusters. (2) Reaction mechanisms. We have used Particle Swarm Optimization (PSO)to discover, without human supervision, the sequence of geometric transformationsthat occur in molecules during chemical reactions (``reaction mechanisms''). We willcreate a new method, based on chemical intuition and optimization techniques, to find a priori(without any DFT calculation) reaction mechanisms. We will find, on a case-by-case basis, whether this mechanism is a good approximation to thelowest-energy reaction path (the true mechanism), and will classify chemical reactions accordingly. (3) Atomistic simulations. We developed a new fitting method for creatinghigh-dimensional PES that is fully automated, does not requirethe user to input a function form, and which works for practically anychemical composition. This PES function mimics an accurate method (DFT) and offers aspeed-up of 4 to 6 orders of magnitude relative to DFT. We will use it to carry outaccurate Monte Carlo (AIMC) simulations where the PES is used with "importance sampling"to give great computational speed-up. We will also take a two-pronged approachto global optimization where we use the PES function for screeninga large number of geometric structures and generate a much smaller subsetfor which the DFT energy gets calculated.Working on those three fronts we will try to uncover the principles thatgovern the relative stability and geometric structure, and the magnetic,electronic and chemical properties of bimetallic clusters. Based on theseprinciples, and novel methods unique to our group, we will design stablenanoalloys for possible applications in catalysis and magneticdata storage devices.