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Using first-principles calculations, we have determined key properties of Ar and Ne in bcc W that relate to the possible bubble formation of implanted Ar and Ne atoms. The most stable interstitial site of Ar/Ne in bcc W is the tetrahedral site, as in the case of H and He. An interstitial atom causes the substantial strain of surrounding W atoms and the low electron-density region. The calculated migration energy of both Ar and Ne is very small, less than 0.2 eV of H. We calculated the binding energies of nearby interstitial atoms and found a strong dependence of atomic species. The attractive interaction between Ne atoms is the largest. Owing to such a small migration energy and a significant interaction between Ar/Ne atoms, interstitial atoms can act as traps for additional atoms and tend to form clusters in the absence of previous damage such as vacancies. The results presented here can explain the possible clustering of implanted atoms in bcc W via self-trapping. [ABSTRACT FROM AUTHOR]

Spectral features of MnK-edge x-ray absorption near-edge structure (XANES) for Li2MnO3 were calculated using the first-principles full projector augmented wave method with the general gradient approximation plus U method. We demonstrated that the U parameter affects the spectral features in the pre-edge region while it does not affect those in the major absorption region. From the comparison with the experimental spectra and those of reference compounds, we showed that the spectral features of MnK-edge XANES and the differences in the valence state can be reproduced well. [ABSTRACT FROM AUTHOR]