The existence of non-stoichiometric uranium oxides is well known. However, many of these possible structures are not well-characterized experimentally because traditional analysis tools fail to easily characterize the structure of systems with low or no translational symmetry. Even stoichiometric uranium oxides such as U3O8, U4O9, and UO3 exhibit complex crystal phases when varying temperature and pressure. Using a combination of genetic algorithms and Density Functional Theory (DFT) calculations, stable or metastable UOx crystals can be identified. Several structure prediction codes already exist that use genetic/evolutionary algorithms to successfully predict novel crystal phases, such as the Genetic Algorithm for Structure Prediction (GASP) and the Universal Structure Predictor: Evolutionary Xtallography (USPEX) codes. USPEX can do additional searches for metastable states using an evolutionary metadynamics algorithm. We have used these structure prediction codes, combined with the Vienna ab initio Simulation Package (VASP) to search the uranium-oxygen system for novel stable and metastable states. By further calculating experimental observables such as the vibrational spectra of low-energy predicted structures, direct comparisons to experimentally obtained data of unknown compounds can be made and unknown experimental samples can potentially be assigned to one of the predicted crystal structures.

Crystal structure prediction: Using genetic algorithms and DFT to search for novel stable and metastable uranium oxides

255th National Meeting (2018)

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