Theoretical Study of Isotope Fractionation Effects in Different Systems Based on First Principles

The study of theoretical calculation work of isotope fractionation effect provides a good theoretical basis for the research of geochemistry and other related disciplines. Numerous scholars use different calculation methods which may lead to the deviation of the calculation results. In this work, we calculated some gases, liquids, and minerals systems by Gaussian software with two different methods, B3LYP/6-311+G(d, p) and HF/3-21G. Theoretical calculation results could be compared with the previous experimental and natural sample measurements in this field. The comparison between theoretical calculation and experimental results could come up with which theoretical method is closer to the results of many kinds of research, and provide a direction for future researchers when choosing to apply the theoretical methods. This study draws some preliminary conclusions as follows: 1. The isotope fractionation effect of isotopologue with light atoms is greater than that with heavy atoms. 2. The isotope fractionation factors are a function of temperature, and these parameters decrease with the temperature increase. 3. The calculations with the HF/3-21G method are not very accurate. The calculations with the B3LYP/6-311+G(d, p) method are closer to the results of many research works than those of the HF/3-21G method.