Hello, A change in allocation has been requested: Requester: zmei (Zhigang Mei) Project: Multilayer_nitride Title: Atomic-scale design of radiation-tolerant multilayer coatings for nuclear applications Description: We use atomistic MD simulations to investigate one of the interface-governed behaviors exhibited by multilayered nanocomposite of ZrN and AlN, i.e., their substantially enhanced resistance to radiation damage compare to pure ZrN or AlN. Results from MD simulation will be compared to experimental ion irradiation studies of multilayered AlN/TiN nanocomposite [Milsosavljevic, J. Phys. D: Appl. Phys. 43 (2010) 65302]. The interatomic potentials for the nitrides are based on the modified embedded atom method (MEAM). However, there is no ternary potential available for ZrN-AlN. We will use the so-called force matching method as implemented in potfit [Brommer, Modelling Simul Mater Sci Eng 15 (2007) 295] to develop such ternary potential. To build a potential suitable for the simulation of a complicated ternary system in a wide ranges of pressure and temperature, we have to prepare an extensive set of reference configurations representing all kinds of interesting stru ctures. Each configuration is a small structure model corresponding to one of the possible states of the ZrN-AlN system. VASP will be used to calculate energy, force and stress of the reference configurations with atoms up to 250. The total computational time for DFT calculations will be about 30000 CPU-hours. Model ZrN-AlN bilayers are constructed in the experimentally observed orientation relation [Milosavljevic, J Phys. D: Appl. Phys. 43 (2010) 065302], in which a ZrN {111} plan neighbors an AlN {0001} plane and an interfacial ZrN <112> direction lies parallel to an AlN <2110> direction. The constituent ZrN and AlN layers are 4.5 nm thick, have periodic boundaries in the interface plane, and terminate in free surfaces away from the interfaces. The ZrN/AlN multilayer nanocomposite can be created in a similar way by stacking 4.5 nm-thick ZrN and AlN crystalline slabs, in which each ZrN or AlN layer contains up to 100000 atoms (22.5×22.5×4.5nm). The layer thickness, number of layers and interface orientation can be controlled in deposition experiments, which will be investigated independently by atomistic simulations. The ZrN-AlN+ZBL potential is used to model collision cascades in in cubic ZrN, hexagonal AlN, and in the vicinity of ZrN-AlN interfaces formed in the multilayer composites. Cascades are initiated by giving a selected atom-the primary knock-on atom (PKA)-a large kinetic energy. The Kinetic energies given to PKAs are chosen to be representative of Ar+ implantation experiments carried out on ZrN-AlN nanocomposites, where the energy of the implanted ions was 200 keV. In the multilayer model systems PKAs are selected from the central layer. For the collision cascade simulations, the first few pico-seconds require extreme fine time step to capture the recombination of point defects, and then nano-second time scale simulations are necessary to reach a thermal equilibrium for the defect structure. By combining all the factors to be studied, we will expect about 25 production jobs. Our initial test shows that a single job needs about 25000 CPU-hours (256 CPU×96 hours). We therefore r equest the total computational time of 650000 CPU-hours. Current: undetermined amount Justification: The used molecular dynamics code LAMMPS has been demonstrated to be cable of simulating millions of atoms using thousands of CPU efficiently. The detailed benchmarks of the parallel efficiency of lammps on different platform can be found from the website of the author http://lammps.sandia.gov/bench.html. With the typical number of CPU (256 CPU) in our MD simulations, the parallel efficiency of LAMMPS on Blues will be above 70%. Requested: 150000 A specific reason has been given: The requested computational time was fully allocated as requested. Meanwhile, DFT calculation for random alloy structures is much more demanding than expected. This needs to be approved and the final allocation amount decided upon. Thank You, The LCRC Accounts System