Hello, A yearly allocation for the LCRC cluster has been requested with the following updated information: Submitter/PI: Weronika Walkosz Project Name: Metastable_Materials Division: MSD Project title: First-principles studies of growth mechanisms for metastable materials Associated funding: ANL Strategic LDRD, DOE Other Systems: NERSC, pnnl-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 at omistic 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 continue our systematic study of the non-equilibrium growth of Group-III nitrides with NH3, In(CH3)3, and Ga(CH3)3 as N, In, and Ga precursors, respectively. So far, we have investigated the interaction of NH3 and its moieties with the (0001) surfaces of InN and GaN, focusing on their adsorption energies and decomposition barriers. The next step in our modeling will be the incorporation of In and Ga from In(CH3)3 and Ga(CH3)3 onto the nitride surfaces. First, gas phase decomposition rates will be calculated for these compounds to establish the precursor composition interacting with the surfaces at relevant conditions. The species will be then placed on the surfaces along with appropriate NHx (x=0-3) precursors and the reaction energies will be calculated. Decomposition barriers for NH3 will be also computed on the nitride surfaces in the presence of the In and Ga species and compared to our earlier calculations on bare surfaces. Additional ly, we are planning to calculate kinetic barriers for NH3 decomposition on strained surfaces since the nitrides are currently grown on substrates with a large lattice mismatch by our experimental collaborators. Surface step edges and kinks will be considered in our modeling as well. Lastly, we will investigate atomic and electronic structure of the (0001) surface of ZrB2, which is a promising substrate for the growth of GaN due to a good lattice match and similar thermal expansion coefficients. Binding sites and energies, and diffusion barriers for adsorbed Ga and NHx species on two different terminations of ZrB2 (0001) surface will be calculated. Also, vibrational frequency calculations will be performed for the lowest energy ZrB2 surfaces in the presence of NHx (x=0-3) and will be compared to the ongoing experimental measurements. The predicted precursor decomposition barriers will be used to develop a kinetic model aiming at optimizing synthesis conditions to grow ni tride materials of much higher quality. All calculations will be performed with Vienna Ab-initio Simulation Package (VASP), using plane wave basis sets and PAW potentials. The kinetic barriers for NH3 on the nitride surfaces and ZrB2 will be computed 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 the outlined calculations. The speed and reliability of the Fusion cluster will allow us to accomplish the work in a timely manner. The calculations of the InN, GaN, and ZrB2 surfaces in the presence of N and In (Ga) precursors will take approximately 48 hours each when ran on 48 processors. At least 50 different structures will be calculated. The frequency calculations for the ZrB2 configurations will take approximately 96 hours each when ran on 48 processors. We are planning to run about 25 of them. The calculations of the reaction energy barriers (NEB), on the other hand, will require about 96 hours each when ran on 48 processors based on our previous work. At least 60 reaction barriers for NH3 decomposition (i) in the presence of In (Ga) precursors, (ii) on strained surfaces and (iii) miscut surfaces will be performed for InN and GaN surfaces. Therefore, a total allocation of 700,000 processor hours will be needed to perform the proposed calculations. Project URL: Current FY Hours Used: undetermined amount New FY Requested allocation: 700000 Q1: 250000 Q2: 150000 Q3: 150000 Q4: 150000 Justification: This work pursues development of models to describe kinetically controlled growth of group-III nitrides based on first-principles approaches. The project is part of Argonne strategic Materials for Energy initiative. Three different surfaces (i.e. the (0001) surfaces of InN, GaN, and ZrB2) will be investigated in detail in the presence of MOCVD precursors. Since VASP does not scale very well beyond 48 processors for our systems, it precludes the use of short-time large-scale capabilities of leadership class computer facilities. In fact, the scaling of the calculations is dramatically reduced with the number of processors beyond 48. The use of Fusion cluster will allow us to overcome the computational challenges posed by the significantly large system sizes necessary for modeling various surfaces as well as decomposition and diffusion processes, which are computationally very demanding. The detailed estimate of the required computer time is given at the end of the project description. Thank You, The LCRC Accounts System