气固氢化反应热力学函数计算的近似方法

An Approximation Method for Calculation of the Thermodynamic Function f or Gas-solid Hydrogenating

在有效原子实势近似下 ,采用Gaussian 98程序及B3LYP/SDD密度泛函方法计算得到了Zr Co和ZrCoH分子的结构及能量E、熵S .在此基础上 ,近似以气态分子总能量中的振动能Ev代替该分子处于固态时的振动能量 ,以电子运动和振动运动熵Sev代替分子处于固态的熵 ,计算了不同温度下固态ZrCo与H2 ,D2 ,T2 反应的热力学函数ΔH ,ΔG ,ΔS 及氢化反应平衡压力 ,导出了氢化反应温度与平衡压力的依赖关系 .计算得出ZrCoH ,ZrCoD ,ZrCoT的生成焓 (3 98—5 98K)分别为 82 .81 ,81 .5 4和 80 .49kJ/mol。

Density functional (B3LYP/SDD) method with relativistic eff ec tive core potential (RECP) have been used to optimize the structure of ZrCo and ZrCoH, and to calculate energy E, entropy S and enthalpy H of ZrCoH(D,T) . Considering the characteristics of different motion types, the vibration energ y or electronic motion and vibration entropy of the molecules is assumed to be t he corresponding values of their solid states. ΔH , ΔS , ΔG and hydrogen isotope equilibrium pressures of the hydrogenating reactions h ave been calculated based on this approximation. The formation enthalpies for Zr CoH, ZrCoD and ZrCoT at temperature from 398 K to 598 K are 82.81, 81.54 and 8 0.49 kJ/ mol, respectively. The results agree with the experimental results. I t is means that the present method is somehow reasonable for studing the thermod ynamic functions of the hydrogen storage materials theoretically.