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。将理论计算的顺铁磁态、铁磁态和反铁磁态的总能量与C14或C15结构的总能量进行比较，理论预测与有关晶体结构稳定性和磁性的实验结果吻合较好。对于非磁性状态，晶体结构几乎是由B原子决定的：Cr、Co或Ni有利于C14，而Mn或Ni有利于C15结构。当A原子按Y、Zr、Nb顺序变化时，晶格间距减小，B原子的磁性按此顺序变弱，这导致了TiFe_2、NbFe_2或Sc_&lt；1-x&gt；Ti_xFe_2等铁Laves相化合物中磁性的五彩缤纷的行为。在Mn Laves相化合物中，唯一具有磁性的是YMn_2，用这个计算合理地解释了其反铁磁态的反常体积变化。用LSD-LMTO-ASA方法系统地研究了R_2Fe_&lt；17&Gt；B(R=Y，Ce，Nd，Gd)的电子结构。磁化强度(30B/FU)和各原子位的磁矩的计算结果与实验符合得很好。同时还研究了RFe2，RFe5和R2Fe17&Gt；(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分布，并与实验结果进行了比较。用LSD-LMTO-ASA方法研究了Si/二硅化物界面的电子结构。

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.