Hello, A change in allocation has been requested: Requester: handany (Handan Yildirim) Project: md_pls_dft_for_TiO2 Title: First Principles and Classical Molecular Dynamics Calculations of Lithium Intercalation into TiO2 Surfaces and Nanostructures Description: The problem is inherently multi-scale in nature, and the ultimate answer to those observed features could only be provided using a multi-scale simulation approach. Thus, we will treat the problem using both DFT and MD simulations. At the first stage of the calculations we will use MD simulations (at low and high temperature – ranging form 300K to 700K) for a long enough time (~ 5ns at the current studies) to observe/learn about the details of the Li diffusion processes in both crystalline and amorphous TiO2 bulk structures at lithium concentrations relevant for battery electrode operation (ranging from 25% to 100% interstitial lithium). Using these observed processes as an input, we will calculate the corresponding energetics, diffusion pathways and dynamics using periodic Density Functional Theory calculations. MD results will also be expected to provide possible differences in the diffusion and dynamics of Li in crystalline and amorphous structures. On the other hand, using DFT, we will explore detailed electronic structures of the crystalline and amorphous TiO2 to understand and validate the observations obtained from MD simulations for both systems. The second phase of these analyses will be devoted to reveal the effect of nano-structuring and morphology on the above-mentioned properties. For this part of the work, we will explore Li diffusion energetics and dynamics in crystalline and amorphous nanotubes and nanoparticles of TiO2 by changing the size, length and diameter (in the case of tube) of these nanostructures. For this stage, we will vastly benefit from the ability of classical MD simulations that allow simulation of several thousands of atoms. We will explore the size effects on Li intercalation properties. The third stage of the calculations will be devoted to investigating electric field effects on the Li diffusion energetics and dynamics on both crystalline and amorphous TiO2. We will apply an electric field less than the break down potential of TiO2 on both crystalline and amorphous structures, and explore the field effects with low and high Li concentrations. Our goal in this part of the study is to separate the effect of field from that of the concentration and thus to evaluate the role of each parameter in Li diffusion. These calculations are expected to provide further insights into the role of field on both crystalline and amorphous structures thus help to explain the observed amorphous to crystalline phase transition. These calculations will be performed using MD simulations at both low and high temperatures, and for ns range simulation times. In preliminary work, we have obtained several results for the diffusion and absorption of Li in TiO2 Anatase bulk both using DFT and MD simulations. Using DFT (the VASP code), we have calculated three absorption energies and diffusion activation barriers for three diffusion processes of Li. We have analyzed the results of MD simulation at both 500K and 700K to identify the possible Li diffusion processes, and used these processes to calculate the corresponding energetics using DFT. Our preliminary DFT results show that Li prefers to sit at the octahedral site at which it is six- coordinated. The diffusion mechanism of Li is observed to facilitate through hopping from an octahedral to octahedral site that leads to the lowest activation energy barrier as compared to those other two processes. We also note that the existence of Li leads a shift in Fermi level as noted in the literature. Lets us note that the presence of oxygen makes our DFT calculations quite expensive since we need to use large enough energy cut off (500eV is used at the current simulations). For sufficient convergence of the total energy of about 100 atoms system with the chosen parameters requires 100 plus ionic iterations. For the recent simulations, we have mostly used 32 CPU’s per job, and at least 5 jobs, on average, run simultaneously; we expect a similar distribution of jobs when running VASP on Fusion. Depending on the requirement for finer converged energies, we will be adjusting these parameters. Note that we will also be exploring Li adsorption and diffusion on other such systems as Anatase and Rutile surfaces, nanoparticles of several sizes, nanotubes, and amorphous TiO2 thus it is inevitable that we require significant computational resources to complete this part of the proposed study. We have also performed preliminary classical MD simulations to study Li diffusion energetics and dynamics under several conditions using the DL-POLY code. Our preliminary results for Li diffusion in Anatase TiO2 bulk provided several insights for Li behavior in such system. Upon relaxation, we find that Li prefers to sit at the octahedral site as observed in our DFT study. We have performed several MD simulations for single Li diffusion at temperatures ranging from 300K to 700K for simulation times ranging from 500ps to 5ns. We find that it is not possible to observe diffusion at low temperature as 300K due to high correlation time of ~1 microsecond reported. However, the diffusion at higher temperatures (500K and above) is observed, and found to facilitate through hopping between octahedral sites. We have also managed to obtain an amorphous TiO2 starting from Anatase bulk, and the obtained amorphous phase is in very good agreement with that of reported in an experimental stu dy. We are currently exploring several such aspects of Li diffusion (in both crystalline and amorphous structures) as concentration, temperature, and field effects to understand the role of each individual parameter in the experimentally observed phase transition. Note that these simulations have to be performed with a very fine timestep (~0.2 fs in general), thus requires long simulation hours even for 5ns. For the current calculations we have systems of nearly 3000 to 5000 atoms. For 5ns simulation, we need 25 millions simulation step, and note that we are exploring the diffusion events at both low and high temperatures. Lets us note that, for system size of 3000-5000 atoms using 0.2fs time step, the simulation of 5ns at low temperatures with Li loaded in the system requires approximately 10 days using 32 CPU’s. We anticipate that we will be running of about 5 to 10 jobs per day to complete this part of the proposed research. Our simulations also indicate that for the ca lculations with field introduced, the required time step is even finer. Our calculations will be extended to study the same phenomenon for the above-mentioned nanostructruced systems thus we will be in need of significant computational resources for the completion of this proposed study. Current: undetermined amount Justification: In roughly three and a half months, we required over 250,000 CPU hours for the combination of MD and DFT calculations that also include testing of classical potential used, and the convergence tests for DFT studies. These calculations have been performed on the CNM’s carbon cluster, but this resource is fully subscribed and is being increasingly used for external user projects. Thus, we require substantial computational resources on Fusion to complete our proposed project. For a full year, we estimate that approximately 550,000 CPU hours will be sufficient. Requested: 300000 A specific reason has been given: I have used about 200000 core-hours approximately for the last six months. I would like to request allocation time to increased to 300000 core-hours. The project involves both DFT and extensive MD simulations that require substantial time. This needs to be approved and the final allocation amount decided upon. Thank You, The LCRC Accounts System