Hello, A yearly allocation for the LCRC cluster has been requested with the following updated information: Submitter/PI: Haiying He Project Name: glassforms Division: MSD Project title: First-principles Calculations of Mineral and Glass Dissolution under Various pH Conditions Associated funding: DOE-NE Other Systems: Science: The dissolution of glass forms in nuclear waste disposal determines their long term stability, which is critical for evaluating disposal scenarios. The dissolution behavior of minerals and glasses has been found to strongly depend on the pH value of the aqueous environment. The delicate balance of ions at the solid-water interface in aqueous solutions is still a big challenge both for accurate computational modeling and for unambiguous experimental measurements. This project aims to develop physical models to simulate the water-borosilicate glass forms interface at the atomic level under various pH conditions and to calculate the rates of dissolution for Si, Al and other constituting elements under acidic, neutral and basic conditions. These studies are based on first-principles calculations. The calculated reaction barriers together with the surface model can then be used to estimate the overall dissolution rates and compare with experimental values. These data wil l also serve as a valuable dataset to feed into kinetic models for better understanding of the dissolution behavior and prediction of dissolution rates. Project 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 free-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. Project URL: Current FY Hours Used: undetermined amount New FY Requested allocation: 800000 Q1: 150000 Q2: 250000 Q3: 200000 Q4: 200000 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 bar rier calculation is 460,800 core hours. In sum, the total requested allocation for this project is 800,000 core hours. Thank You, The LCRC Accounts System