摘要/Abstract

本工作建立了一种量子化学的组合方法并应用于研究在硫和汞复合污染地区, 汞及其化合物是否会参与和驱动硫酸气溶胶形成. 该方法采用Molclus Genmer模块生成数以百万计的巨量团簇初始结构, 用自洽紧束缚GFN2-xTB方法预优化, 再用B3PW91-D3(BJ) DFT方法重新优化, 结合能经ωB97M-D3(BJ)校正后计算出团簇的热力学函数, 以其生成过程Gibbs自由能变大小排序, 获得团簇稳定序列及其对应的结合能和热力学函数. 然后用该方法研究了汞及其化合物、硫酸和水生成的8种团簇模型共计240万个结构, 结果表明HgSO₄, HgO等汞的极性化合物以及Hg₂²⁺和 Hg²⁺能够促进硫酸气溶胶的形成, 而Hg以及无极性的HgCl₂和Hg₂Cl₂对硫酸气溶胶成核的影响较小. 这一结论对硫、汞复合污染环境下, 硫酸气溶胶成核机制探讨提供了有价值的预测.
关键词: 量子化学, 组合方法, 硫酸气溶胶, 汞, 热力学函数
Haze weather has been occurring frequently in recent years, and studies have shown that its formation mechanism is related to the nucleation of sulfuric acid aerosols. How mercury and its compounds affect the formation and growth of sulfuric acid aerosols is completely unclear in polluted areas where sulfur and mercury coexist. In order to explore this problem theoretically, we established a new quantum chemistry combination method. Millions of cluster structures are generated by using the Molclus Genmer module. The cluster geometries are preliminarily optimized by the GFN2-xTB method and sorted according to the Gibbs free energy changes of the cluster generation process. The top 100 optimized structures were re-optimized using the B3PW91-D3(BJ) method. In order to accurately calculate the binding energy of clusters, we established a small benchmark set based on the composition and structural characteristics of the clusters studied in the project, and used the CCSD(T)/CBS method to calculate the binding energy of each cluster model in the benchmark set. Using the binding energy as a standard, the best method selected from 42 DFT methods is ωB97M-D3(BJ). The binding energy calculated by B3PW91-D3(BJ) is corrected by the results of the ωB97M-D3(BJ) method to obtain an accurate thermodynamic function value. It is worth mentioning that the combined method was used to study a total of 2.4 million structures in 8 cluster models formed by mercury and its typical compounds, sulfuric acid and water. The results show that polar compounds of mercury such as HgSO₄ and HgO, together with Hg₂²⁺ and Hg²⁺, can promote sulfuric acid aerosol formation, while Hg and non-polar HgCl₂ and Hg₂Cl₂ have almost no effect on the nucleation of sulfuric acid aerosol. In addition, we found that the conclusion holds true for the temperature interval of the troposphere at standard atmospheric pressure. This conclusion provides valuable predictions for the studies on sulfuric acid aerosol nucleation mechanisms under the combined sulfur and mercury pollution environment.
Key words: quantum chemistry, combination method, sulfuric acid aerosols, mercury, thermodynamic function


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