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Analytic energy gradients for the orbital-optimized second-order M?ller-Plesset perturbation theory

机译:轨道优化的二阶Mller-Plesset微扰理论的解析能量梯度

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Analytic energy gradients for the orbital-optimized second-order M?ller-Plesset perturbation theory (OMP2) are presented. The OMP2 method is applied to difficult chemical systems, including those where spatial or spin symmetry-breaking instabilities are observed. The performance of the OMP2 method is compared with that of second-order M?ller-Plesset perturbation theory (MP2) for investigating geometries and vibrational frequencies of the cis-HOOH~+, trans-HOOH~+, LiO_2, C3+, and NO _2 molecules. For harmonic vibrational frequencies, the OMP2 method eliminates the singularities arising from the abnormal response contributions observed for MP2 in case of symmetry-breaking problems, and provides significantly improved vibrational frequencies for the above molecules. We also consider the hydrogen transfer reactions between several free radicals, for which MP2 provides poor reaction energies. The OMP2 method again exhibits a considerably better performance than MP2, providing a mean absolute error of 2.3 kcal mol~(-1), which is more than 5 times lower than that of MP2 (13.2 kcal mol~(-1)). Overall, the OMP2 method seems quite helpful for electronically challenging chemical systems such as symmetry-breaking molecules, hydrogen transfer reactions, or other cases where standard MP2 proves unreliable. For such systems, we recommend using OMP2 instead of MP2 as a more robust method with the same computational scaling.
机译:提出了轨道优化的二阶Mller-Plesset微扰理论(OMP2)的解析能量梯度。 OMP2方法适用于困难的化学系统,包括观察到空间或自旋对称性破坏不稳定性的化学系统。将OMP2方法的性能与二阶M?ller-Plesset微扰理论(MP2)的性能进行了比较,以研究顺式-HOOH〜+,反式-HOOH〜+,LiO_2,C3 +和NO的几何形状和振动频率_2个分子。对于谐波振动频率,OMP2方法消除了由于对称破坏问题而观察到的MP2异常响应贡献所引起的奇异性,并为上述分子提供了显着改善的振动频率。我们还考虑了几个自由基之间的氢转移反应,为此MP2提供了较差的反应能量。 OMP2方法再次表现出比MP2更好的性能,提供的平均绝对误差为2.3 kcal mol〜(-1),比MP2的平均绝对误差(13.2 kcal mol〜(-1))低5倍以上。总体而言,OMP2方法似乎对电子挑战性化学系统(如对称性破坏分子,氢转移反应或标准MP2证明不可靠的其他情况)很有帮助。对于此类系统,我们建议使用OMP2而不是MP2作为具有相同计算比例的更强大的方法。

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