Hello, A change in allocation has been requested: Requester: jgreeley (Jeffrey Greeley) Project: DFT_corrosion Title: Electrochemical corrosion and oxidation of metal surfaces from first principles Description: We intend to use periodic DFT calculations to study corrosion (dissolution and oxidation) of transition metal surfaces. It is essential to develop an understanding of these processes in order to be able to control the long-term stability of metal electrodes in fuel cells; such electrodes are known to degrade in successive oxidation/reduction cycles over extended periods of fuel cell operation. In particular, building upon our expertise in simulations of the dissolution thermodynamics of close-packed and kinked metal surfaces1, 2, we will develop simple, electrode potential-dependent computational models of metal corrosion (including both surface oxidation and dissolution) on defect-rich single crystal surfaces and on small (d ~ 1nm) nanoparticles. The first step will be to determine the binding energies of atomic O and OH, as a function of coverage, on a single-crystal kinked Pt surfaces; Pt(763) and Pt(854) will be chosen for this purpose. Numerous configu rations will be considered for each adsorbate coverage, and the lowest-energy configurations at each coverage will be input into an atomistic thermodynamic formalism (essentially a simplified Grand Canonical Monte Carlo technique)3 to determine the O coverage as a function of electrode potential. These results will then be compared to tabulated values of the equilibrium dissolution potential of Pt as a function of the Pt2+ ion concentration in the surrounding solution; with this analysis, it will be possible to estimate the approximate coverages of surface O and OH that are present at the thermodynmically reversible potential on these surfaces, thereby providing important insights into the interplay between surface oxidation and platinum loss by dissolution. By studying how O and OH decorate the step edges at these higher potentials, it will also be possible to obtain semi-quantitative insight into passivation and place exchange mechanisms that may be operative in various potential ranges. A natural extension of this initial work will be to consider the effect of Au decoration of the kink edges on the oxidation and dissolution thermodynamics of these kinks; this type of decoration is expected to passivate the kink features. The computational procedure for the oxidation studies will be identical to that described above for the unalloyed kinked surfaces, but it is anticipated that the oxidation will be substantially suppressed by the presence of the Au atoms. Additionally, it is expected that Au will increase the reversible dissolution potential of the Pt kinks; although experimental data are not available to confirm this prediction, the DFT-based technique that we have developed to predict shifts in dissolution potentials due to alloying1 can provide semi-quantitative estimates of these changes. A final component of this study will be to contrast the corrosion properties of Pt nanoparticles of ~1 nm diameter with the corresponding properties of the kinked single crystal surfaces. As a first step, we have already identified the optimal shapes of Pt clusters with 51-55 atoms; this size range was chosen since it contains clusters with approximately the diameter mentioned above (1 nm). These shapes were identified using an EMT-based potential, combined with an extensive Monte Carlo search; the best geometries obtained with this procedure were subsequently refined with DFT calculations. The energetic differences between the various cluster sizes provide a quantative estimate of the dissolution potentials of these clusters (such data are not available experimentally). The subsequent analysis of oxidation, which will be the focus of this study, will involve optimization of the oxygen coverage of these particles as a function of potential; as with the single crystals, thi s will be accomplished using an atomistic thermodynamic technique. The final step will be to generate detailed thermodynamic phase diagrams of the dissolution and oxidation states of the clusters as a function of potential; this analysis will, in turn, permit us to obtain a thorough understanding of the interplay between oxidation and dissolution in nanoparticle corrosion processes. These computational studies will be performed in collaboration with Nenad Markovic (ANL/MSD). The computational requirements of the proposed research will be substantial. Test calculations with the Dacapo code have indicated that the relatively large kinked Pt surfaces chosen for study in this project require approximately 15 hours per total geometric optimization on 24 cores (the practical parallelization limit of Dacapo calculations) on computer clusters similar to Fusion. Considering that a large number (~1000-1500) of O, OH, and Pt configurations will need to be considered to understand the potential-dependent dissolution and oxidation of the kinked Pt surfaces and nanoparticles, we are requesting 500,000 core hours for the proposed project. Dacapo has been running successfully on Jazz for the past ~2.5 years, and we have not experienced any significant performance problems. Current: undetermined amount Justification: The computational requirements of the proposed research will be substantial. Test calculations with the Dacapo code have indicated that the relatively large kinked Pt surfaces chosen for study in this project require approximately 15 hours per total geometric optimization on 24 cores (the practical parallelization limit of Dacapo calculations) on computer clusters similar to Fusion. Considering that a large number (~1000-1500) of O, OH, and Pt configurations will need to be considered to understand the potential-dependent dissolution and oxidation of the kinked Pt surfaces and nanoparticles, we are requesting 500,000 core hours for the proposed project. Requested: 200000 A specific reason has been given: The project is producing exciting results, but we have realized that a number of additional configurations (beyond what we originally anticipated) need to be considered to completely describe the system in detail. This needs to be approved and the final allocation amount decided upon. Thank You, The LCRC Accounts System