Patkowski Konrad, Szalewicz Krzysztof, Jeziorski Bogumił
Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
J Chem Phys. 2006 Oct 21;125(15):154107. doi: 10.1063/1.2358353.
We present an extension of many-body symmetry-adapted perturbation theory (SAPT) by including all third-order polarization and exchange contributions obtained with the neglect of intramonomer correlation effects. The third-order polarization energy, which naturally decomposes into the induction, dispersion, and mixed, induction-dispersion components, is significantly quenched at short range by electron exchange effects. We propose a decomposition of the total third-order exchange energy into the exchange-induction, exchange-dispersion, and exchange-induction-dispersion contributions which provide the quenching for the corresponding individual polarization contributions. All components of the third-order energy have been expressed in terms of molecular integrals and orbital energies. The obtained formulas, valid for both dimer- and monomer-centered basis sets, have been implemented within the general closed-shell many-electron SAPT program. Test calculations for several small dimers have been performed and their results are presented. For dispersion-bound dimers, the inclusion of the third-order effects eliminates the need for a hybrid SAPT approach, involving supermolecular Hartree-Fock calculations. For dimers consisting of strongly polar monomers, the hybrid approach remains more accurate. It is shown that, due to the extent of the quenching, the third-order polarization effects should be included only together with their exchange counterparts. Furthermore, the latter have to be calculated exactly, rather than estimated by scaling the second-order values.
我们提出了多体对称适配微扰理论（SAPT）的一种扩展，纳入了在忽略单体内部相关效应的情况下得到的所有三阶极化和交换贡献。三阶极化能自然地分解为诱导能、色散能以及混合的诱导 - 色散能分量，在短程范围内会因电子交换效应而显著淬灭。我们提出将总的三阶交换能分解为交换 - 诱导能、交换 - 色散能以及交换 - 诱导 - 色散能贡献，它们为相应的单个极化贡献提供淬灭作用。三阶能量的所有分量均已用分子积分和轨道能量表示。所得到的公式对以二聚体为中心和以单体为中心的基组均有效，并已在通用的闭壳层多电子SAPT程序中实现。已对几个小分子二聚体进行了测试计算并给出了结果。对于色散束缚的二聚体，纳入三阶效应消除了对涉及超分子Hartree - Fock计算的混合SAPT方法的需求。对于由强极性单体组成的二聚体，混合方法仍然更精确。结果表明，由于淬灭程度的原因，三阶极化效应应仅与其交换对应项一起纳入。此外，后者必须精确计算，而不是通过按比例缩放二阶值来估计。
