Mg_2NiQ_6(Q=H,D,T)体系的热力学氢同位素效应

Thermodynamic Hydrogen Isotopic Effect of Mg_2NiQ_6 (Q=H, D, T)

为研究Mg2NiQ4(Q=H,D,T)体系的热力学氢同位素效应,基于量子力学第一原理,采用密度泛函与赝势平面波相结合的方法,计算了Mg2NiQ6(Q=H,D,T)体系的声子色散谱,利用声子色散谱得到了热力学函数.利用文献报道的氢同位素气体分子的热力学数据,采用热力学方法分析了Mg2Ni吸氢形成Mg2NiQ6的同位素效应.研究结果表明,Mg2Ni吸氢的同位素效应主要是原子相对振动的频率不同导致的.CaF2结构的Mg2NiQ6的氢同位素效应随温度升高由负同位素效应转变为正同位素效应.

To study the thermodynamic hydrogen isotopic effect in Mg2NiQ4 （Q=H, D, T）, a calculation based on first-principles and pseudo-potential plain waves combined with density function theory to determine the phonon dispersion properties of Mg2NiQ6 （Q=H, D, T） was undertaken. Thermodynamic functions were thus obtained. The hydrogen isotope effect was investigated using thermodynamic methods during the process of hydrogen isotope absorption by Mg2Ni wherein it was converted into Mg2NiQt. Gibbs free energies of hydrogen isotopes that were reported in literature were employed for this calculation. Results show that the hydrogen isotopic effect originates from differences in opposite atomic vibration frequencies. As the temperature increases, the isotopic effect of the Mg2NiQ6 with a CaF2 structure changes from a negative isotopic effect to a positive isotopic effect.