基于密度泛函理论计算SF₆分子结构及性质
Calculation of SF₆molecule structure and properties based on density functional theory
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摘要: 为探究外电场对 SF?分子电子结构与性质的调控机制,为其在绝缘、电场控制等领域的应用提供理论支撑,本文采用密度泛函理论(DFT)中的 M062X/6-311g** 方法优化 SF?分子基态结构,分析沿 X 轴施加 - 0.03~0.03 a.u. 外电场时,分子偶极矩、平均静态极化率、Mulliken 电荷布居、前线轨道能量、能隙、红外光谱及激发态性质的变化规律；通过杂化 CIS 方法计算 SF?分子前 15 个激发态的激发能、激发波长及振子强度。结果表明：无外电场时,SF?为非极性分子,结构对称稳定；外电场作用下,分子对称性降低,偶极矩增大并转变为极性分子,几何结构稳定性下降；平均静态极化率显著增大,利于提升气体绝缘性能；Mulliken 电荷发生定向转移,电子云分布重构；前线轨道能隙减小,化学反应活性增强；红外光谱特征吸收峰增多,振动模式更丰富；激发能与激发波长呈先增后减的非单调变化,激发态 7-9 振子强度非零,为外电场调控激发波长提供了可能。Abstract: : :T To investigate the regulation mechanism of external electric fields on the electronic structure and properties of SF? molecules and provide theoretical support for their applications in insulation, electric field control, and other fields, this study optimized the ground-state structure of SF? molecules using the M062X/6-311g** method based on density functional theory (DFT). The variation laws of molecular dipole moment, average static polarizability, Mulliken charge population, frontier orbital energy, energy gap, infrared spectrum, and excited-state properties were analyzed when an external electric field of -0.03~0.03 a.u. was applied along the X-axis. Additionally, the excitation energy, excitation wavelength, and oscillator strength of the first 15 excited states of SF? molecules were calculated via the hybrid CIS method. The results show that without an external electric field, SF? is a nonpolar molecule with a symmetric and stable structure. Under the action of an external electric field, the molecular symmetry decreases, the dipole moment increases, and the molecule transforms into a polar molecule, leading to a reduction in geometric structure stability. The average static polarizability significantly increases, which is conducive to improving the gas insulation performance. Mulliken charges undergo directional transfer, resulting in the reconstruction of electron cloud distribution. The energy gap of frontier orbitals decreases, enhancing chemical reactivity. The number of characteristic absorption peaks in the infrared spectrum increases, indicating richer vibration modes. The excitation energy and excitation wavelength exhibit non-monotonic changes of first increasing and then decreasing, and the oscillator strengths of excited states 7-9 are non-zero, which provides the possibility for regulating the excitation wavelength via external electric fields.
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