Papers by Keyword: Supercell

Abstract: The outcome of the density functional theory (DFT) technique within the supercell's framework of La₂CuO₄ (LCO) are reported. We evaluatedlocal dipolar fields of muon's position inside LCO assuming dipolar interaction is occurred by varying the supercell's size. We found out that the field on proposed muon's trapping positions were known to be not affected so much by supercell's size and still fairly larger than the experimental data. Our results suggest that the inclusion of quantum effects of implanted muon and the electronic spin are required to explain experimental data.

Abstract: From 31 May to 1 June 2010, serious super high precipitation multi-cells caused convectional rainstorm in central region of Guangxi. The heaviest hour rainfall was 92mm, the heaviest rainfall for 48 hours was 503.9mm. The storms developed in the southwest warm moist wind and moved rightly. The radar reflectivity displayed several bow echoes moving from west to east along the 850hPa shear line. A line echo wave pattern developed. At 2.4°elevation angle, the maximum radar reflectivity of supercell reached 69dBz. The cross section of reflectivity showed that the 40dBz reflectivity core reached 9km in height, indicating a deep updraft. The radial velocity imagery showed with the mesocyclone features such as inverse wind area, the positive and negative velocity pairs. The VAD profile showed the deep warm-wet layer before the storm occurred. The 12m/s southwest wind reached 8km in depth. About 2 hours before the rainstorm, the VAD profile showed double dry region. When the double dry region appeared half hour later, the first rainstorm occurred. The numerical simulation analysis results indicated that the high precipitation multi-cell storms was produced and moved along the vortex path.

Abstract: TiO2 has been intensively studied as a wide band-gap transition metal oxide partially due to the multi-valence nature of its cation. Here, density-functional theory calculations within the supercell approximation are carried out to determine the preferred charge state of point defects in rutile TiO2. The first component of this work is to investigate the dependence of the defect formation energies on supercell size and the electrostatic Makov-Payne correction. The results show that the Makov-Payne correction improves the convergence of defect formation energies as a function of supercell size for positively charged titanium interstitials and negatively charged titanium vacancies. However, in the case of positively charged oxygen vacancies, applying the Makov-Payne correction gives the wrong sign for the defect formation energy correction. This is attributed to the shallow nature of the transition levels for this defect in TiO2. Finally, we combine the calculated defect formation energies with thermodynamic data to evaluate the influence of temperature on the relative stabilities of point defects. The results indicate that when the Makov- Payne correction is applied, a stable charge transition occurs for titanium interstitials. In addition, as the temperature increases, the dominant point defect in TiO2 changes from oxygen vacancies to titanium interstitials.