报告题目: DFT+U Study of Actinide Dioxides　 报告人: 王保田 博士(山西大学物理电子工程学院)时间: 2012年11月23日(星期五),下午2:30地点: 山西大学物理电子工程学院报告厅　Abstract:  Calculations of actinide dioxides (AO₂, A=Th, U, Np, or Pu) illustrate that the 5f electrons in U,Np, and Pu have significant effects on their compounds’ electronic structure, and need use the local-densityapproximation (LDA)+U approach, while for thorium with only one 5f electron, GGA method can give properresults. The LDA+U approach with U=4 eV can prominently improve upon the conventional DFT and, thus,can provide a satisfactory qualitative electronic-structure description comparable with experiments for oxidesof U, Np, or Pu. Based on the electronic-structure analysis, we demonstrate that the Th-O, U-O, Np-O, andPu-O bonds can be interpreted as displaying a mixed ionic/covalent character. Pu-O, U-O, and Np-O bondshave stronger covalency than the Th-O bond. The ionicity of Th-O bond is the largest. Results of elastic constantsand phonon dispersions indicate that the ambient phase of AO₂ is stable. For ThO₂ and PuO₂, the Fm-3m to Pnmatransition occurs at 26.5 and 24.3 GPa, respectively. Isostrctural transitions in the pressure ranges of 80-130 GPaand 75-133 GPa are predicted for these two kinds of actinide dioxides, respectively. The Pnma phase of PuO₂will occur a metallic transition around 133 GPa. Through first-principles computational tensile test on PuO₂, weobtain the mechanical features along different crystalline orientations. The theoretical tensile strengths are firstlycalculated. We find that the strong ionic/covalent character of Pu-O bond is weakened by tensile stain and PuO₂will exhibit an insulator-to-metal transition.
      Along with this results, some new calculations on UO₂ will be presented.　　上述报告结束后增加教学研究报告:题目: 惠斯顿电桥实验的背景反思

报告人: 宋伟 老师