关于立方晶体Mg_2NiH_4结构中复合体[NiH_4]的几何构型

On the Configuration of the [NiH_4] Complex in Cubic Mg_2NiH_4 Structure

用相对论密度泛函法研究了立方晶体Mg2NiH4结构中复合体[NiH4]的几何构型．晶体的环境用一个“切断”（Cut－off）的Madelung势来模拟．计算中分别假设了一个平面四边形NiH和一个四面体NiH的构型．对于平面四边形构型，计算的Ni-H键长及力常数与实验值相符；但对四面体计算的键长太短而力常数太大．研究结果表明；立方Mg2NiH4结构中对复合体[NiH4]的选择是平面四边形构型，而不是四面体．

The configuration of the [N1H4] complex in cubic Mg2NiH4 structure has been investigated by using relativistic density-functional method The crystalline environment was simulated by a cut-off type Made1ung potential. A square planar configuration of NiHi and a tetrahedral configuration of NiH are assumed, respectively in the calculations. For the square planar configurati0n, a good agreement of the calculated bond length and force constant with experimental ones was obtained. However, the calculation on the tetrahedral configuration yielded too short Ni-H bond length and too large Ni-H force constant. The comparison between the ca1culated results and experimenta1 ones gives a clear preference of the square NiH configuration over the tetrahedral NiH configuration in the cubic Mg2NiH4 structure.