The performance of the MP2.5 method (MP2 augmented by scaled MP3 correction) is tested for the set of atmospheric reactions including both closed- and open-shell species. The reactions include series of halogen substituted hydrocarbons CH_nX_4-n (n = 1–3, X = Cl, Br, I) reacting with OH radical. Both the UHF and ROHF reference wave functions for the open-shell molecules are considered. MP2/cc-pVTZ optimized geometries were used for the calculation of the reaction energies. The accuracy of MP2.5 is discussed in terms of differences between MP2.5/cc-pVTZ and CCSD(T)/cc-pVTZ energies. Simple a priori diagnostic based on the analysis of the coupled-cluster excitation amplitudes calculated at lower CCSD/cc-pVDZ level is introduced. The method seems to be a promising extension of MP2.5 from the realm of intermolecular interactions to chemical reactivity.

测试了MP2.5方法（通过按比例缩放的MP3校正增强了MP2）的性能，以应对包括封闭壳和开壳物种在内的一系列大气反应。反应包括与OH自由基反应的一系列卤素取代的烃CH _n X _4-n（n = 1-3，X = Cl，Br，I）。考虑了开壳分子的UHF和ROHF参考波函数。MP2 / cc-pVTZ优化的几何结构用于计算反应能。根据MP2.5 / cc-pVTZ和CCSD（T）/ cc-pVTZ能量之间的差异来讨论MP2.5的精度。简单的先验介绍了一种基于对在较低CCSD / cc-pVDZ水平下计算出的耦合簇激励幅度进行分析的诊断方法。该方法似乎是MP2.5从分子间相互作用的领域到化学反应性的有希望的扩展。