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用密度泛函方法B3LYP/6-31G对甲烷、氘代甲烷和各种氚代甲烷进行几何构型全优化,前两者优化的结果与实验值吻合。用上述方法对甲烷、氘代甲烷和氚代甲烷分子进行了分子的振动基频和热力学性质计算。计算结果表明各种氘代甲烷的标度后振动频率的计算值与实验值的最大相对偏差为-2.9％,最小的相对偏差为0.1％。分子等容热容和熵随着氘取代原子数的增加而增加;而零点能和焓却随之减小。
The geometrical configurations of methane, deuteromethane and various tritiated methane were all optimized by density functional method B3LYP / 6-31G. The results of the first two optimization are in good agreement with the experimental data. The molecular vibrational fundamental frequency and thermodynamic properties of methane, deuteromethane and tritiated methane molecules were calculated by the above method. The calculated results show that the maximum relative deviation between calculated and measured vibrational frequencies of various kinds of deuterated methane is -2.9% and the minimum relative deviation is 0.1%. Molecular heat capacity and entropy increase with the increase of the number of deuterium substitution atoms, while the zero energy and enthalpy decreases.