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: Weronika Walkosz Applicant's institution: ANL Applicant's division: MSD Project Name: Metastable_Materials Project title: First-principles studies of growth mechanisms for metastable materials Associated funding: ANL Strategic LDRD, DOE Other Systems: Carbon, PNL-Chinook Science: The main objective of the project is to develop first-principles models describing the growth of Group-III nitrides in order to establish a firm basis for far-from-equilibrium nitride synthesis in a wide range of compositions. In particular, the growth of InxGa1-xN alloys will be extensively studied in this work because of their widespread applications in solid-state lighting, optoelectronics, and photovoltaics. Although metal organic chemical vapor deposition (MOCVD) is the most efficient and clean deposition process for production of nitride solid-state devices, the growth process for InxGa1-xN via this technique has been observed to display a complex behavior characterized by self-sustaining spatiotemporal chemical oscillations between nanocrystalline islands of InN and elemental In droplets. While these results suggest that the nitrogen activity produced by surface-catalyzed ammonia (NH3) decomposition may be responsible for the observed unusual behavior, an atomistic model of the gas phase and surface chemistries, and catalytic reactions that govern such behavior needs to be developed. We propose calculations aimed at development of a kinetic model, which will help optimize synthesis conditions to grow InxGa1-xN materials of much higher quality for solid-state lighting. The parameters of the model describing oscillatory behavior of InN islands/In droplets during the growth will be determined from the results. Identification of rate-limiting reaction steps will lead to optimization of synthesis conditions and precursors based on this model. The results of the modeling will be validated by comparison to the experimental data obtained in ANL. This model is expected to be applicable to describe kinetically controlled processes in synthesis of other materials. Project description: We will perform first-principles calculations for the adsorption and diffusion of NH3 on GaN, InN, and In surfaces through reaction intermediates such as NH2, NH, N, and H. The simulations will be performed with Vienna Ab-initio Simulation Package (VASP), using plane wave basis sets and PAW potentials. We will first model surfaces of GaN, InN, and In metal in the presence of NH3 to determine the most stable surface sites/configurations for the absorbed NH3 and its decomposed species. Next, diffusion and dissociation pathways of NH3 on various surfaces will be studied by calculating energy barriers using the Nudged Elastic Band Method. The scale of the proposed calculations exceeds small computer cluster capacity. Therefore, we are requesting the LCRC resources to perform a computational study of NH3 on GaN, InN, and In metal. The speed and reliability of the Fusion cluster will allow us to finish the work in a timely manner. The calculations of a dsorption and decomposition of NH3 on different surfaces will take approximately 48 hours each when ran on 64 processors. At least 50 different structures will be calculated. The calculations of the reaction energy barriers (NEB), on the other hand, will require about 96 hours each when ran on 80 processors as determined by on our previous experience with these types of calculations on semiconductors. At least 42 reaction barriers need to be calculated to validate a diffusion model. Therefore, a total allocation of ~ 475,000 processor hours will be needed to perform the proposed calculations. Project URL: Requested allocation: 475,000 Justification: The requester has used 7669 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