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: Alejandro Rebola Applicant's institution: ANL Applicant's division: MSD Project Name: polar_interfaces Project title: Polar Interfaces for Enhanced Ionic Conductivity Associated funding: US Department of Energy, Office of Science-Basic Energy Sciences Division of Materials Sciences and Engineering Other Systems: NERSC (120,000) Science: LaGaO3 (LGO) is one of the most remarkable ionic conductors discovered in the last years. When either doped with Mg or Sr, the ionic conductivity of LGO reaches values of 0.1 S/cm, at an even lower working temperature (1073 K) than that of yttria stabilized zirconia (Y/ZrO2). However, one of the disadvantages of doping is that interactions between dopant ions and their charge-compensating defects can lead to the formation of clusters capable of “trapping” the migrating species. In order to avoid the drawbacks of doping and to achieve enhanced ionic transport in LGO -where oxygen vacancies are the dominant carriers- we propose the use of polar interfaces as a way to induce a vacancies enrichment layer in LGO. We plan to model polar interfaces comprising LGO and other perovskites with a matching lattice parameter, such as CaHfO3 (CHO). By creating negatively charged interfaces, and by using perovskites composed by single valence elements, we expect the formation of oxygen vacancies as compensating defects to be a very likely compensation mechanism. Calculations in order to asses the different compensating mechanisms, formation and activation energies of oxygen vacancies, as well as other quantities of interest will be performed within the Density Functional Theory formalism and by using state of the art computational software. Project description: The calculations outlined below will be performed by using the VASP and Quantum Espresso codes. According to our experience, these codes scale up to ~48 cores in the type of calculations considered in the present proposal. In order to investigate the properties of negative LGO/CHO interfaces, the following calculations will be performed: 1) Calculations for LGO and CHO bulk systems. Relaxations for both internal and lattice parameters will be performed in both bulk structures before modeling the interface. Defect formation energies for both vacancies and interstitials will be calculated in each material for different supercell sizes in order to ensure convergence. This part of the calculation would require a total of 10,000 core-hours. 2) Polar LGO/CHO interfaces are going to be considered for different number of LGO and CHO unit cells in order to determine critical thickness for defect formation. Systems with and without defects are going to be considered. In the latter different locations and configurations are going to be calculated in order to find the most stable ones. Given the size of the largest supercells to be considered (~300 atoms) and the different possible configurations for defects (vacancies, interstitials, cation substitution), this part of the calculation would require -according to our previous experience in similar systems- a total of 250,000 core-hours, approximately. 3) Once determined the most stable configuration for defects, a Nudge Elastic Band (NEB) calculation will be performed in order to determine the activation energy for oxygen vacancies in the LGO/CHO heterostructure. NEB calculations, since the require optimizations over several images, are usually costly. Our previous experience indicates that this could be done with a total of 50,000 core-hours. 4) Finally, single point calculations at a denser k-point grid and with a higher cutoff will be performed in order to obtain density of states, band structure, potential profiles and more accurate defect formation energies. This part of the calculation is not very demanding and could be done with a total of 10,000 core hours, approximately. In conclusion, we estimate that in order to accomplish our project it will be necessary a total of 320,000 core-hours, approximately. Project URL: Requested allocation: 320000 Q1: 100000 Q2: 100000 Q3: 100000 Q4: 20000 Justification: The requester has used undetermined amount 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