基于密度泛函理论的外电场下C_3F_8微观特性的研究

全氟丙烷(C_3F_8)作为一种拥有较低温室效应的SF_6替代气体,被国内外学者广泛研究.为了从分子层面上揭示全氟丙烷在外电场作用下微观特性的变化情况,采用密度泛函理论中的M06-2X方法,在6-31G(d)基组水平上优化得到了C_3F_8的基态稳定构型.分析了不同外电场(0-0.020 a.u.)对C_3F_8分子的结构、Highest Occupied Molecular(HOMO)、Lowest Unoccupied Molecular(LUMO)、能隙、键级的影响,并研究了全氟丙烷分子的激发态能、波长、振子强度.结果表明,在所加电场范围内,随着电场强度的增大,C_3F_8分子最高占据轨道能级逐渐增大,最低空轨道能级逐渐减小,能隙E_G逐渐减小, C_3F_8分子的化学活性增强;C_3F_8分子中的C-C键的Mayer Bond Order (MBO)值随电场强度的增大均出现增大的情况,分子的稳定性降低;C_3F_8分子激发态的激发能总体上呈现出减小的趋势,激发态的波长总体上则呈现出增大的趋势,表明在外电场的作用下,全氟丙烷分子变得越来越容易激发.

Study on the Microscopic Characteristics of C3F8 under External Electric Field Based on Density Functional Theory

Perfluoropropane (C3F8), as a substitute gas of SF6 with low greenhouse effect, has been widely studied by domestic and foreign scholars. In order to reveal the change of the Micro-properties of perfluoropropane under external electric field at molecular level, the ground-state stable configuration of C3F8 was optimized at 6-31G(d) base level by using M06-2X method of density functional theory. The effects of different external electric fields (0-0.020a.u.) on the structure, HOMO level, LUMO level, energy gap and bond level of C3F8 molecule were analyzed. The excited state energy, wavelength and oscillator strength of perfluoropropane molecule were studied. The results show that the maximum occupied orbital energy level increases, the lowest unoccupied orbital energy level decreases, the gap EG decreases and the chemical activity of C3F8 molecule increases with the increase of electric field intensity. The MBO value of C-C bond in C3F8 molecule increases with the change of electric field intensity, and the stability of C3F8 molecule decreases. With the increase of external electric field intensity, the excitation energy of C3F8 molecule''s excitation state decreases on the whole, while the excitation wave length increases on the whole, which indicates that perfluoropropane molecule becomes more and more easy to excite under the action of external electric field.