Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201, USA.
J Phys Chem A. 2011 Nov 17;115(45):13201-9. doi: 10.1021/jp207381t. Epub 2011 Oct 11.
Non-nuclear local maxima, or attractors, of electron density are a rare but very interesting feature of the electron density distribution in molecules and solids. Recently, non-nuclear attractors (NNAs) and the corresponding pseudoatoms of electron density have been identified with the quantum theory of atoms in molecules for some anionic clusters formed by several polar solvent molecules and an excess electron bound in either a solvated-electron or dipole-bound fashion. This contribution reports a detailed study of the topology of the electron density for a series of dipole-bound water cluster anions, as calculated with Hartree-Fock, Møller-Plesset perturbation theory, and coupled-cluster methods together with basis sets augmented with extra diffuse basis functions to accommodate the excess electron. For dipole-bound clusters, electron densities obtained with insufficient inclusion of electron correlation effects and tight basis sets feature a well-pronounced pseudoatom due to the excess electron, which ultimately disappears when a higher level of electronic structure theory and a more diffuse basis set are used. On the other hand, for solvated-electron clusters, where the excess electron is surrounded by solvent molecules, the existence of NNAs does not seem to be an artifact of the method employed, but rather a genuine feature of the electron density distribution. Pseudoatoms of electron density thus appear to be an exclusive feature of confined environments and are unlikely to be found on the tip of a cluster dipole or on solid surfaces.
电子密度的非核局域极大值（或吸引子）是非分子和固态电子密度分布中一种罕见但非常有趣的特征。最近，利用分子轨道量子理论，在一些由几个极性溶剂分子和以溶剂化电子或偶极束缚方式结合的额外电子形成的阴离子团簇中，已经确定了非核吸引子（NNAs）和相应的电子密度拟原子。本贡献报告了对一系列偶极束缚水团簇阴离子的电子密度拓扑结构的详细研究，这些研究是使用 Hartree-Fock、Møller-Plesset 微扰理论和耦合簇方法以及带有额外弥散基函数的基组来计算的，以适应额外电子。对于偶极束缚团簇，由于额外电子的存在，当电子相关效应和紧密基组的包含不足时，电子密度会呈现出一个明显的拟原子，而当使用更高水平的电子结构理论和更弥散的基组时，这个拟原子最终会消失。另一方面，对于被溶剂分子包围的溶剂化电子团簇，NNAs 的存在似乎不是所采用方法的人为产物，而是电子密度分布的真实特征。因此，电子密度的拟原子似乎是受限环境的特有特征，不太可能在团簇偶极的尖端或固体表面上找到。
