Hello, A new project on the LCRC cluster has been requested. Please forward the information on to the LCRC Allocation sub-committee. Applicant's name: Haiying He Applicant's institution: ANL Applicant's division: Materials Science Project Name: glassforms Project title: First-principles Calculations of Mineral and Glass Dissolution under Various pH Conditions Associated funding: DOE Other Systems: Science: 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-silicate (either in crystalline or 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 will also serve as a valuable dataset to feed into micro-kinetic models for better understanding of the dissolut ion behavior and prediction of dissolution rates. Project description: As a model system, we have chosen first to study the dissolution of a mineral – orthoclase (KAlSi3O8) under various pH conditions and then to extend our knowledge to other minerals or glasses. The first part is to develop a physical model to predict the hydrogen coverage on a surface as a function of the pH value of the aqueous solution. This is done by calculating the variation of free energy as one brings a proton from solution to the surface. First-principles calculations are employed for the surfaces and tabulated ionization potential and solvation energy data for aqueous protons. The surface Si sites are, for instance, categorized into three types – neutral (≡SiOH), protonated (≡SiOH2+) and deprotonated (≡SiO-). The second part is to calculate the reaction barrier of breaking the Si-O-Si bond or the Si-O-Al bond at different surface sites. The energy required to break the Si-O-Si(Al) bond is also different depending upon their coordina tion number to the bulk. 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 Nudge Elastic Band method). The calculated reaction barriers together with the surface site distribution determined from the surface model can then be used to estimate the dissolution rates. We will be able to validate our theoretical results by comparison with experimental measurements at ANL. We will also consider different surface orientations and defective surfaces. Therefore, the calculations will determine dependence of reaction rates on changes in pH values, surface orientations, and the presence of defects on surface. This project primarily uses the density-functional-theory (DFT) implemented electronic structure code VASP. The system sizes of our calculations are usually around 100-200 atoms. VASP has been tested to scale very well in parallel processing on Fusion. The optimum number of processors used for these systems is 32-64 processors per calculation. Project URL: Requested allocation: 783,360 Justification: The first-principles calculations will be carried out using the electronic-structure code VASP. A single optimization calculation takes 48 hours on 32 processors. We are considering 10 perfect and defective surfaces/interfaces, each requiring 15 optimization calculations to derive their free energies as a function of pH, thereby to determine the surface structure interfaced with solvent. Therefore, the total required computer time for this part is 230,400. The second part is to calculate the detailed reaction pathways under acidic, neutral and basic conditions. The energy required to break the Si-O-Si(Al) bond is again differentiated by their coordination numbers with the bulk material (varying from 1 to 4). It takes about 48 hours on 160 processors (5 images) to calculate a reaction barrier. Therefore, the total estimated computer time for this part is 552,960. In sum, the total requested allocation for this project is 783,360 processor hours. The requester has used 0 hours of their initial startup project. In addition to approving an initial amount, please specify a Category and Subcategory for this project. For a list of the current selection of approved categories, please see: https://wiki.lcrc.anl.gov/wiki/Processes/Categories Once the Allocation committee has approved the project, please go to the Project Management page to create it: https://accounts.lcrc.anl.gov/projects.php Thank You, The LCRC Accounts System