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Wyświetlanie 1-3 z 3
Tytuł:
Local structure and cohesive properties of mixed thorium and uranium dioxides calculated by "ab initio" method
Autorzy:
Dąbrowski, L.
Szuta, M.
Powiązania:
https://bibliotekanauki.pl/articles/147874.pdf
Data publikacji:
2012
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
uranium
thorium dioxide
DFT+U
LDA
GGA
local structure
cohesive properties
bulk modulus
Opis:
Density functional theory (DFT) results of calculations of the mixed thorium and uranium dioxide Th1-xUxO2 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 plus or minus 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.
Źródło:
Nukleonika; 2012, 57, 1; 101-107
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
„Ab initio” study of helium atoms immobilization in UO2 crystals
Autorzy:
Dąbrowski, L.
Szuta, M.
Powiązania:
https://bibliotekanauki.pl/articles/146654.pdf
Data publikacji:
2012
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
uranium
dioxide
DFT+U
LDA
GGA
ABINIT
over-barrier jumps
incorporated helium
harmonic oscillator
Opis:
We present density functional theory (DFT) calculation results concerning the uranium dioxide crystals with a helium atom incorporated in the octahedral interstitial position. "Ab initio" calculations were performed using the Wien2k program package. For comparison, a pseudo-potential approach in the generalized gradient approximation was applied using the ABINIT program package. To compute the unit cell parameters 13 atom super-cell was chosen. Parameters of the potential barrier, which the helium atom has to overcome while jumping to the next octahedral interstitial position, were calculated by the help of both the program packages. The results, obtained using two different program packages, are shown in the table and presented graphically. For the so described parameters, the quantum mechanical movement of the helium atom around the equilibrium position is considered. The parameters of Schrödinger's equation are collected in Table 2, while the results of mean square deviation and thermal occupation of energetic levels are presented in a graph. It is established that the helium atoms are located (with an accuracy of several percent of lattice constant) nearby the equilibrium position and form a local bound state. Applying a two site-model, we evaluated the time for an over-barrier jump. Graphically presented results show that the helium atom over-barrier jump is not possible even for temperatures as high as 1200 K. Influence of potential barrier height on the jump time was also considered.
Źródło:
Nukleonika; 2012, 57, 3; 337-343
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Diffusion of helium in the perfect uranium and thorium dioxide single crystals
Autorzy:
Dąbrowski, L.
Szuta, M.
Powiązania:
https://bibliotekanauki.pl/articles/147700.pdf
Data publikacji:
2013
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
uranium
thorium dioxide
diffusion
tunneling
DFT+U
generalized gradient approximation (GGA)
potential barrier
incorporated helium
Opis:
We present quantum-mechanical evaluation of helium diffusion coefficient in the crystalline UO2 and ThO2. Parameters assignment of Schrödinger’s equation were done using the crystal field potentials which were obtained applying the density functional theory (DFT). “Ab initio” calculations were performed using the Wien2k program package. To compute the unit cell parameters the 13 atom super-cell was chosen. Applying two-site model we evaluated the time for an over-barrier jump and diffusion of interstitial He. The obtained values for diffusion coefficient are compared with the experimentally obtained values and with the theoretical values of other authors. In addition, it is simultaneously shown that helium diffusion in these materials is a quantum diffusion.
Źródło:
Nukleonika; 2013, 58, 2; 295-300
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-3 z 3

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