Energy Band Calculation of the Compounds with Rare Earth and Transition metals

1.在LSD近似框架下，用LMTO-ASA方法系统地研究了Laves相化合物AB_2（A=Y，Zr，Nb;B=Cr，Mn，Co，Fe）的电子结构.通过对C14或C15结构的帕拉铁磁、铁磁和反铁磁态的总能量的计算，与有关晶体结构稳定性和磁性的实验结果相比较，理论预测符合得很好。B原子的存在几乎决定了C_（14）态的晶体结构：Cr、Co或Ni倾向于C_（14）结构，Mn或Ni倾向于C_（15）结构。当A原子按Y、Zr、Nb的顺序变化时，晶格间距减小，B原子的磁性变弱，导致了铁Laves相化合物如TiFe_2、NbFe_2或Sc_ Ti_xFe_2中磁性的彩色行为<1-x>。在Mn Laves相化合物中，唯一的磁性相是YMn_2，该计算合理地解释了其在反铁磁态的反常体积变化.用<17>LSD-LMTO-阿萨方法系统地研究了R_2Fe_ B（R=Y，Ce，Nd，Gd）的电子结构.磁化强度（30 _B/FU）和各原子位磁矩的计算结果与实验符合得很好。在<17>同一谱线上研究了RFe_2、RFe_5和r_2Fe_（R=Y，Ce，Gd）的电子结构.用LSD-FLAPW方法计算了LaB_6和CeB_6的电子结构和正电子湮没剖面，并与实验结果进行了比较.采用LSD-LMTO-阿萨方法研究了Si/Disilicides界面的电子结构。

1. The electronic structures of Laves phase compounds AB_2 (A=Y,Zr,Nb;B=Cr,Mn,Co,Fe) were investigated systematically by the LMTO-ASA calculation within the framework of the LSD apprpximation. Comparing the calculated total energy for hypothetical para-, ferro- and antiferromagnetic state with the C14 or C15 structure, the theoretical predictions are in good agreement with the experiments concerning the stability of the crystal structure and the magnetism. For the nonmagnetic state, the crystal structures are almost determines by the B atom: Cr, Co or Ni favours the C14 and Mn or Ni favoures the C15 structure. When the A atom changes in the order Y, Zr and Nb, the lattice spacing decreases and the magnetism of the B atom becomes weak in this order, which leads to the colorful behaviours of the magnetism in iron Laves phase compounds such as TiFe_2, NbFe_2 or Sc_<1-x>Ti_xFe_2. In Mn Laves phase compounds, the only magnetic one is YMn_2, whose anomalous volume change in the antiferromagnetic state was reasonably explained by this calculation.2. The electronic structures of R_2Fe_<17>B(R=Y,Ce,Nd,Gd) were investigated systematically by the LSD-LMTO-ASA calculation. The calculated results of the magnetisation (30 _B/FU) and the magnetic moments at each atomic sites were in good agreement with the experiments. The electronic structures of RFe_2, RFe_5 and r_2Fe_<17> (R=Y,Ce,Gd) were also investigated in the same line.3. The electronic structures and the positron-annihilation-profiles of LaB_6 and CeB_6 were calculated by the LSD-FLAPW method and compared with the experiments.4. The electronic structures of Si/Disilicides interfaces were investigated by the LSD-LMTO-ASA calculation.