基于密度泛函理论的SF_6替代气体筛选方法的研究综述

Review of Screening Sulfur Hexafluoride Alternative Gases Based on Density Functional Theory

环境友好型SF_6替代气体的相关研究目前受到了极大的重视。文中介绍了国内外基于密度泛函理论(density functional theory, DFT)SF_6替代气体筛选方法的相关研究,详细阐述了预测未知绝缘气体的绝缘强度和液化温度的筛选方法,分析了计算选择的泛函、基组对计算结果的影响,指出了在M06-2X/6-311+G(3df)级别下计算值与实验值偏差较小。对比了预测时选择的气体分子微观参数对预测结果的影响,分析表明分子表面静电势与液化温度和绝缘强度相关性较强。提出了卤族元素取代对气体分子的绝缘强度和液化温度的影响及其变化规律,即随着卤族元素相对分子质量的增大,绝缘强度和液化温度也相应升高的变化规律。此外,电子碰撞电离的碰撞截面是筛选完成后进行绝缘特性研究的重要参数,通过对比基于密度泛函理论在DM公式和改进后的DM公式下的碰撞截面值,结果表明改进后的DM公式提高了计算结果的准确性。最后指出了未来研究发展的方向,考虑气体的绝缘、灭弧、环保等多个方面建立了SF_6替代气体的综合评价体系。

Studies about environment-friendly SF6 alternatives have been paid more attentions recently. In this paper, the related researches on the method of sulfur hexafluoride substitutes based on density functional theory(DFT) are introduced. The screening methods for predicting the electric strength and liquefaction temperature of unknown insulating gas are described in detail, and the selected functional and basic set for calculation are analyzed. The influences of them on the calculation results indicate that the deviation between the calculated value and the experimental value is small at the M06-2 X/6-311+G(3 df) level. The influences of the microscopic parameters of the gas molecules selected during the prediction on the prediction results are compared. The analysis shows that the surface electrostatic potential is closely related to the liquefaction temperature and electric strength. The effects of halogen substitutions on the electric strength and liquefaction temperature of gas molecules and their changing rules are proposed. That is, as the relative molecular mass of halogens increases, the electric strength and liquefaction temperature also increase accordingly. In addition, the collision cross section of electron impact ionization is an important parameter for the study of insulation properties after screening.We compare the values of the collision section under the DM formula and the modified DM formula based on the density functional theory. The results show that the modified DM formula improves the accuracy of the calculation results. Finally,the direction of future research and development is pointed out, and a comprehensive evaluation system for SF6 alternative gas should be established under consideration of gas insulation, arc extinguishing, and environmental protection.