50K for this quarter POC: Larry Curtiss pri: 1 Cat: P:Nano On Mon, Feb 16, 2015 at 06:22:30PM -0600, [email protected] wrote:

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: Anh Ngo Applicant's institution: ANL Applicant's division: MSD Project Name: AlN Project title: A DFT study of reaction pathways of NH3 decomposition on AlN (0001) surface Associated funding: Strategic LDRD Other Systems: Science: Strong demands for high-efficiency light-emitting diodes in the deep-ultraviolet and sensors have led to renewed interest in the growth of high-quality AlN. However, the growth of high quality AlN is extremely difficult due to the weak surface migration of Al adatoms. The most commonly used growth technique for AlN films is metalorganic chemical vapor deposition (MOCVD) with ammonia serving NH3 as the nitrogen precursor. Identification of kinetic pathways that produce high nitrogen activity during precursor surface decomposition and Al precursor migration pathways are essential to understanding and optimizing growth of metastable nitrides such as AlN using reactive vapors. In this study, we plan to further address these proposed determining factors to catalytic activity by calculating reaction thermodynamics and kinetics of the decomposition of NH3 on the technologically relevant (0001) surface of AlN via H dissociation as well as a new pathway involving H transfer between the reduced NHx (x = 1???2) species on the surface. We will also investigate decomposition and migration of Al precursors. These studies will provide valuable information toward rational designs of catalysts with high activity and selectivity for the growth of high-quality AlN under MOCVD conditions. This work will help interpretation of in-situ x-ray experiments on AlN growth at the APS.

Project description: Structure optimizations of the adsorbate-free (0001) surface of AlN were already investigated using (2 ?? 2) surface unit cells. We will perform density functional theory (DFT) calculations to determine structure, bonding, and reaction energies of the adsorbed species. Periodic boundary condition (PBC) will be imposed in order to maintain periodicity of the solid support. Gradient corrected PBE density functional will be used for these calculations. The Climbing Nudged Elastic Band (cNEB) method of Henkelman and coworkers will be used to calculate transition states and activation barriers for formation of different surface species. Each structure in the supported (0001) surface of AlN typically involves ~100 atoms. To obtain accurate reaction energies and barriers, rigorous density functional theory (DFT) calculations are needed. We intend to carry out the DFT calculations using the VASP package. VASP is currently available on Blues cluster and scaling with number of processors is well established. For the MPI version of VASP with the system size of ~100 atoms, a good performance was observed up to 32 processors. Energy optimization in VASP takes approximately 750 CPU hours and we plan approximately 100 of such calculations for different adsorbate geometries. The Climbing Nudged Elastic Band (cNEB) calculation (with 5 to 7 images) takes approximately 1600 CPU hours and we plan to run 60 of these calculations to find reaction pathways. So our total request is 750*150 + 60*1600 = 208,500 core hours

Industry partnership: none Project URL: Requested allocation: 208500 Q1: 0 Q2: 50000 Q3: 80000 Q4: 78500 Justification: Storage requirements: no additional storage needed

The requester has used undetermined amount hours of their initial startup project.

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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

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