晶态Ca_3C_(60)与Ca_5C_(60)的能带结构研究

Band Structure Studies for Crystalline Ca_3C_(60) and Ca_5C_(60)

用三维EHMO晶体轨道程序分别对Ca3C60，Ca5C60进行了能带结构的计算．计算结果表明，Ca3C60没有导电性，能隙约为0．9eV；而在Ca5C60的能带结构中，费米面刚好穿过半满带，表明Ca5C60是导体；同时在费米面附近有较大的态密度值，表明Ca5C60与K3C60等类似，具有较高的超导转变温度．电荷分析表明，在这两种情况下，钙原子的4s电子基本上全转移到C60上，C60分子可形成一个稳定的带6到10个电子的负离子．

Three dimsional EHMO crystai orbital calculations for crystalline Ca3C60and Ca5C60 are reported. The ground state of partially doped Ca3C60 is found to beinsulating with an indirect energy gap of 0.5eV. In contrast, Ca5C60 forms a metallicconducting phase with a set of three half-filled bands crossing the Fermi level which isfound to be located close to the peak of the density of state. The character of crystalorbitals near the Fermi-level for both Ca3C60 and Ca5C60 is completely carbon-like. Inboth cases, the Ca atoms are almst fully ionized and C60 molecules can form a stablenegative charge state with sir to ten additional electrons. The projected DOS of Ca atomsnear the Fermi-level and the overlap populations between Ca and C are negiectible.