NUKLEONIKA 2012, 57(1):101-107
## LOCAL STRUCTURE AND COHESIVE PROPERTIES OF MIXED THORIUM AND URANIUM DIOXIDES CALCULATED BY "AB INITIO" METHODLudwik Dąbrowski, Marcin Szuta
National Centre for Nuclear Research (NCBJ), 7 Andrzeja Sołtana Str., 05-400 Otwock/Świerk, Poland Density functional theory (DFT) results of calculations of the mixed thorium and uranium dioxide Th _{1–x}U_{x}O_{2} for the following mole ratio x = 0, 0.25, 0.75 and 1 are presented and discussed. “Ab initio” calculations were performed using the Wien2k program package. To compute the unit cell parameters the 12 atom super-cell were chosen. The lattice parameters were calculated through minimization of the total energy by the change of lattice parameters and atom displacement within the unit cell. Calculations were performed for five different exchange energy approximations EXC with and without corrective orbital potential U, and obtained lattice constants are presented graphically and compared with experimental data. It is established that the initially assumed oxygen location within the unit cell ± 0.25 of the mixed compounds are not their equilibrium positions. The oxygen atoms within the unit cell undergo dislocation in the (111) direction. So, the distances oxygen-uranium are smaller than the distances oxygen-thorium. The change of local structure is presented graphically and appropriate parameters values are given in Table. The bulk modulus and the cohesive properties are also counted and shown graphically.
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