John Low, Does this look reasonable? If it is we might provide 120K. Ray On 7/10/12 1:43 PM, "[email protected]" <[email protected]> wrote:

Hello,

A change in allocation has been requested:

Requester: hahe (Haiying He) Project: glassforms Title: First-principles Calculations of Mineral and Glass Dissolution under Various pH Conditions Description: Task I: The task of our research is to include the bulk water effect in the process of glass and mineral dissolution. In the past year, we have calculated hydrolysis reaction barriers of the Si-O-Si bridges and the Si-O-Al bridges at surface sites of orthoclase feldspar (KAlSi3O8) as a model system in different protonation states – neutral (≡SiOH), protonated (≡SiOH2+) and deprotonated (≡SiO-) using the Nudge Elastic Band (NEB) method. In most of the calculations, we have only considered a single H2O attack on the Si-O-Si or Al-O-Si bridge that causes bond rupture with the simultaneous H2O dissociation. Studies of the bulk water effect will determine the role of proton shuttle in aqueous solution and the entropic effect of water. Both effects contribute to the free energy reaction barriers. This task will be accomplished by including explicit H2O molecules in a large supercell and performing constrained molecular dynamics (MD) simulations. Hereby, the f ree-energy profile is a thermodynamic integration over the restoring forces along a parameterized reaction coordinate using the rare-event ensemble technique, which is newly implemented in VASP. We will also use this technique to determine the chemical potentials of protons in solution for the surface site distribution model which we have developed.

Task II: The second task for this year is to extend our study from a model crystalline material to glasses. Using initial structures from classical molecular dynamics, we will continue with first-principles calculations of reaction energies and barriers. Multi-component amorphous structures are some complexities that we need to address in the modeling of glasses. It suggests that we need large supercells and a large number of sampling points. The major components that we will consider in glasses are Si, Al, B (network formers) and Na, Ca (network modifiers). We will carry out similar investigations in terms of the surface protonation and hydrolysis reaction barriers under various pH conditions for bridges involving these elements. The properties that we are going to calculate in this part include structures and energies of reactants, intermediates and products, as well as reaction barriers (based on the NEB method). In some cases, we will validate results using smaller clus ters at high levels of ab initio theory such as CCSD(T) as implemented in NWChem and Gaussian09 packages. The calculated reaction barriers together with the surface site distributions determined from the surface model will then be used in kinetic modeling to calculate the dissolution rates.

This project will primarily use the density functional theory (DFT) implemented in electronic structure code VASP. The system sizes of our calculations ranges from 100 to 300 atoms. VASP has been tested to scale very well in parallel processing on Fusion. The optimum number of processors used for these systems is 16-64 processors per calculation.

Current: undetermined amount Justification: The first-principles calculations will be carried out using the electronic-structure code VASP. In Task I, ab initio MD simulations are conducted, where each trajectory runs for 30-50 ps and it takes 16 processors to run for 96-160 hours (average 2048 core hours per trajectory). We will need to run 100 trajectories for five sets of calculations. That requires 200,048 core hours. In Task II, NEB calculations are conducted to calculate the reaction pathways for a variety of composing elements under acidic, neutral and basic conditions. A single optimization calculation takes 48 hours on 32 processors. We are considering 30 supercell samplings of silicate glasses including multiple components (Si, Al, B, Na, K). The calculation for possible reactants, intermediates, products will take about 138,240 core hours. It takes about 48 hours on 160 processors (5 images) to calculate a reaction barrier along the reaction pathway. The total estimated computer time for barr ier calculation is 460,800 core hours. In sum, the total requested allocation for this project is 800,000 core hours.

Requested: 150000

A specific reason has been given: More allocation is needed to complete the research task.

This needs to be approved and the final allocation amount decided upon.

Thank You, The LCRC Accounts System

----------------------------------------- Ray Bair Computing, Environment, and Life Sciences Argonne National Laboratory and the University of Chicago TCS Building 240, Room 4122 9700 South Cass Avenue Argonne, IL 60439 email: rbair(at)anl.gov Phone: (630)252-5751