Fukui Institute for Fundamental Chemistry, Kyoto University, Nishi-hiraki cho, Takano, Sakyo-ku, Kyoto 606-8103, Japan.
J Comput Chem. 2012 Mar 5;33(6):617-28. doi: 10.1002/jcc.21993. Epub 2012 Jan 6.
Evaluation of intermolecular distance and binding energy (BE) of van der Waals complex/cluster at ab initio level of theory is computationally demanding when many monomers are involved. Starting from MP2 energy, we reached a two-step evaluation method of BE of van der Waals complex/cluster through reasonable approximations; BE = BE(HF) + sum Mi> Mj{BE (Mi- Mj)(MP2 or MP2.5) - BE(Mi-Mj)(HF)} where HF represents the Hartree-Fock calculation, Mi, Mj, etc. are interacting monomers, and MP2.5 represents the arithmetic mean of MP2 and MP3. The first term is the usual BE of the complex/cluster evaluated at the HF level. The second term is the sum of the difference in two-body BE between the correlated and HF levels of theory. This equation was applied to various van der Waals complexes consisting of up-to-four monomers at MP2 and MP2.5 levels of theory. We found that this method is capable of providing precise estimate of the BE and reproducing well the potential energy surface of van der Waals complexes/clusters; the maximum error of the BE is less than 1 kcal/mol and 1% in most cases except for several limited cases. The origins of error in these cases are discussed in detail.
当涉及到许多单体时，在从头算理论水平上评估范德华复合物/团簇的分子间距离和结合能（BE）在计算上是非常耗费资源的。从 MP2 能量开始，我们通过合理的近似达到了范德华复合物/团簇的 BE 的两步评估方法；BE = BE（HF）+ sum Mi> Mj{BE (Mi- Mj)(MP2 或 MP2.5) - BE(Mi-Mj)(HF)}，其中 HF 代表 Hartree-Fock 计算，Mi、Mj 等是相互作用的单体，而 MP2.5 表示 MP2 和 MP3 的算术平均值。第一项是在 HF 水平上评估复合物/团簇的通常 BE。第二项是相关和 HF 理论水平之间的两体 BE 差异的总和。该方程适用于在 MP2 和 MP2.5 理论水平下由多达四个单体组成的各种范德华复合物。我们发现，该方法能够提供 BE 的精确估计，并很好地再现范德华复合物/团簇的势能面；在大多数情况下，BE 的最大误差小于 1 kcal/mol 和 1%，但在某些情况下除外。在这些情况下，详细讨论了误差的来源。
