VQ2(Q=H, D, T)热力学氢同位素效应的理论研究

Theoretical Study on Thermodynamic Hydrogen Isotope Effect of VQ2 (Q=H, D and T)

摘要:

基于量子力学第一性原理，采用赝势平面波函数与密度泛函结合的方法，计算并研究V、VH2、VD2、VT2体系的晶格动力学特征及热力学函数，采用热力学方法分析钒吸氢生成VQ2(Q=H，D，T)的热力学同位素效应。晶格动力学性质研究表明，VQ2的热力学同位素效应主要是氢同位素在钒晶格中的振动频率不同导致的。VQ2生成反应在10~1000 K的温度范围内标准吉布斯自由能变 由－50 kJ·mol-1近似线性上升至140 kJ·mol-1。平衡压力与温度关系表明，在高于常温的条件下，平衡压力随温度急剧升高；钒吸附氢同位素生成二氢化钒在整个温度范围内均表现为负同位素效应

Abstract:

Based on ab-initio principle and pseudo-potential plain wave function combined with density function theory, crystal lattice dynamical characteristics and thermodynamical functions of V, VH2, VD2 and VT2 were calculated. The thermodynamical isotope effect was analyzed based on those calculated data. Calculation results show that both difference of vibration frequency of atoms in VQ2 (Q=H, D and T) and difference of oscillation frequency of hydrogen isotopes are mainly responsible for the hydrogen isotope effect. The standard Gibbs free energy change of the absorption reaction rises from –50 kJ/mol to 140 kJ/mol with the temperature increasing from 10 K to 1000 K. The equilibrium pressure climbs drastically when temperature is higher than room temperature. Within the whole temperature range, only inverse hydrogen isotope effect is found