Department of Chemistry, Rice University, Houston, Texas 77005, USA.
Phys Chem Chem Phys. 2009 Nov 14;11(42):9677-86. doi: 10.1039/b910905f. Epub 2009 Aug 26.
We have been investigating the combination of a short-range density functional approximation with long-range random phase approximation (RPA) correlation, where the direct RPA correlation is constructed using only Coulomb (i.e., not antisymmetrized) two-electron integrals. Our group's recently demonstrated connection between RPA and coupled cluster theory suggests investigating a related method: second-order Møller-Plesset perturbation theory correlation (MP2) constructed using only Coulomb integrals. This new "JMP2" method is related to the scaled-opposite-spin SOS-MP2 approximation [Y. Jung, R. C. Lochan, A. D. Dutoi and M. Head-Gordon, J. Chem. Phys., 2004, 121, 9793], which is also constructed using only Coulomb integrals. While JMP2 and SOS-MP2 yield identical results for closed shell systems, they have important differences for open shells. We show here that both JMP2 and SOS-MP2 provide a reasonable treatment of long-range correlation when combined with a short-range exchange-correlation functional. Remarkably, JMP2's explicit inclusion of (approximate) like-spin correlation effects provides significant improvements over SOS-MP2 for thermochemistry.
我们一直在研究将短程密度泛函近似与长程随机相位近似（RPA）相关联，其中直接 RPA 相关仅使用库仑（即未反对称）双电子积分来构建。我们小组最近在 RPA 和耦合簇理论之间展示的联系表明，需要研究一种相关的方法：仅使用库仑积分构建的二阶 Møller-Plesset 微扰理论相关（MP2）。这种新的“JMP2”方法与缩放相反自旋 SOS-MP2 近似[Y. Jung，R. C. Lochan，A. D. Dutoi 和 M. Head-Gordon，J. Chem. Phys.，2004，121，9793]有关，该方法也仅使用库仑积分构建。虽然 JMP2 和 SOS-MP2 对于闭壳系统产生相同的结果，但它们对于开壳系统有重要的区别。我们在这里表明，当与短程交换相关函数结合使用时，JMP2 和 SOS-MP2 都可以为长程相关提供合理的处理。值得注意的是，JMP2 对（近似）同自旋相关效应的明确包含为热力学提供了比 SOS-MP2 显著的改进。
