Theoretical Study on Electronic Band Structureand Physical Properties if Ternary Compounds

用LAPW方法计算了插层化合物A_xTiS_2 （A =过渡金属、银和碱金属）和三元金属间化合物Mn_2Sb、Mn_3GaC和Fe_7Se_8的电子vand结构和总能量。对于插入银的化合物Ag_x TiS_2，银原子的电子态与基体材料的电子态发生了强烈的杂化，但由于杂化而产生的内聚能增益很小。另一方面，碱性金属原子只向宿主材料提供电子。与过渡金属嵌层化合物相比，Ag_xTiS_2和碱金属嵌层化合物的客体原子与主体材料之间的化学键相对较弱。从总能量计算中证实，abc -叠层结构比ab -叠层结构更稳定，有利于Ag_xTiS_2.2。三元金属间化合物Mn_2Sb， Mn_3GaC和Fe_7Se_8 (1) Mn_2Sb：从晶格常数a和c的函数计算中，发现铁磁态比反铁磁态更稳定。沿a轴的线压缩性评估值大于沿c轴的线压缩性评估值。(2) Mn_3GaC：发现反铁磁态各磁位磁矩的大小及其对磁矩体积的依赖性大于铁磁态。在较大体积侧，反铁磁相比铁磁相更稳定。（39） Fe_7Se_8：在铁磁态下，晶体学上不相等的铁位点上的磁矩几乎相等。由态的电子密度计算得到的光发射谱和光电导率谱与观测值吻合较好。

Electronic vand strucurures and total energies are calculated for intercalated compounds A_xTiS_2 (A = transition-metals, silver, and alkaline metals) and trnary intermetallic compounds Mn_2Sb, Mn_3GaC, and Fe_7Se_8 by using the LAPW method.1. A_xTiS_2 (A = transition-metals, silver, and alkaline metals) For the silver-intercalated compound Ag_x TiS_2 the selectronic states of silver atoms hybridize strongly with those of the host material, but a cohesive energy gain due to the hybrideization is rather small. On the other hand, the alkaline metal atoms only donate electrons to the host material. The chemical bonds between guest atoms and the host material are relatively weak for Ag_xTiS_2 and the alkline-metal-intercalated compounds compared with the transition-metal-intercalated compounds. From the total energy calculation it is confirmed that the ABC-stacking structure is more stable than the AB-stacking is favorable for Ag_xTiS_2.2. Ternary intermetallic compounds Mn_2Sb, Mn_3GaC, and Fe_7Se_8 (1) Mn_2Sb : From the total energies calculated as a function of the lattice constants, a and c, it is found that the ferrimagnetic state is more stable than the antiferromagnetic state. The evaluated value of the linear compressibility along the a-axis is larger than that along the c-axis. (2) Mn_3GaC : It is found that both the magnitude of the magnetic moment at each maganese site and its volume dependence are larger for the antiferromagnetic state than those for the ferromagnetic state. Further, the antiferromagnetic phase becomes more stable than the ferromagneric state in larger volume side. (39 Fe_7Se_8 : In the ferrimagnetic state, the magnetic moments at crystallographically inequivalent iron sites have almost the same values with each other. The photoemission and the optical conductivity spectra clculated from the electronic density of states are in good correspondence with the observations.