Heßelmann Andreas
Lehrstuhl für Theoretische Chemie, Universität Erlangen-Nürnberg, Egerlandstr. 3, 91058 Erlangen, Germany.
Beilstein J Org Chem. 2018 May 2;14:979-991. doi: 10.3762/bjoc.14.83. eCollection 2018.
The quantum-chemical description of the interactions in water clusters is an essential basis for deriving accurate and physically sound models of the interaction potential for water to be used in molecular simulations. In particular, the role of many-body interactions beyond the two-body interactions, which are often not explicitly taken into account by empirical force fields, can be accurately described by quantum chemistry methods on an adequate level, e.g., random-phase approximation electron correlation methods. The relative magnitudes of the different interaction energy contributions obtained by accurate ab initio calculations can therefore provide useful insights that can be exploited to develop enhanced force field methods. In line with earlier theoretical studies of the interactions in water clusters, it has been found that the main contribution to the many-body interactions in clusters with a size of up to = 13 molecules are higher-order polarisation interaction terms. Compared to this, many-body dispersion interactions are practically negligible for all studied sytems. The two-body dispersion interaction, however, plays a significant role in the formation of the structures of the water clusters and their stability, since it leads to a distinct compression of the cluster sizes compared to the structures optimized on an uncorrelated level. Overall, the many-body interactions amount to about 13% of the total interaction energy, irrespective of the cluster size. The electron correlation contribution to these, however, amounts to only about 30% to the total many-body interactions for the largest clusters studied and is repulsive for all structures considered in this work. While this shows that three- and higher-body interactions can not be neglected in the description of water complexes, the electron correlation contributions to these are much smaller in comparison to the two-body electron correlation effects. Efficient quantum chemistry approaches for describing intermolecular interactions between water molecules may therefore describe higher-body interactions on an uncorrelated Hartree-Fock level without a serious loss in accuracy.
水团簇中相互作用的量子化学描述是推导用于分子模拟的水相互作用势的准确且符合物理原理模型的重要基础。特别是，经验力场通常未明确考虑的两体相互作用之外的多体相互作用的作用，可以通过适当水平的量子化学方法准确描述，例如随机相位近似电子相关方法。因此，通过精确的从头算计算获得的不同相互作用能贡献的相对大小可以提供有用的见解，可用于开发增强的力场方法。与早期关于水团簇中相互作用的理论研究一致，已发现对于尺寸高达(n = 13)个分子的团簇，多体相互作用的主要贡献是高阶极化相互作用项。与此相比，对于所有研究的系统，多体色散相互作用实际上可以忽略不计。然而，两体色散相互作用在水团簇结构的形成及其稳定性中起着重要作用，因为与在非相关水平上优化的结构相比，它导致团簇尺寸明显压缩。总体而言，无论团簇大小如何，多体相互作用约占总相互作用能的(13%)。然而，对于所研究的最大团簇，电子相关对这些相互作用的贡献仅占总多体相互作用的约(30%)，并且对本工作中考虑的所有结构都是排斥的。虽然这表明在描述水络合物时三体及更高体相互作用不可忽略，但与两体电子相关效应相比，电子相关对这些相互作用的贡献要小得多。因此，用于描述水分子间分子间相互作用的高效量子化学方法可以在非相关的哈特里 - 福克水平上描述更高体相互作用，而不会在准确性上有严重损失。
