Nature of chemical bond in view of electron density distributions and a new expression for cohesive mechanism between atoms in metalcompounds

空间电子密度分布p(R)的知识对于全面理解物质中原子之间化学键的性质是非常重要的。为了方便起见，已经提出了几种分析p(R)的方法。例如，遵循Mulliken布居分析方法，计算重叠布居和轨道布居，并将其用作原子之间化学相互作用的衡量标准。这种相互作用也可以用电子密度的拉普拉斯量▽^2p(R)来表征。然而，尽管做了很大的努力，关于每种物质共有的p(R)特征的信息却很少。在这里，我们展示了电子密度极小值p&lt；min&gt；和原子或离子半径r&lt；min&gt；其中包括气体(H_2，O_2)，水(H_2O)，金刚石(C)，金属(Fe，Al)，半导体(Si，Ge)，氧化物(MgO，Al_2O_3，SiO_2，BaTiO_3)，碱卤化物晶体(NaC，KCl)和金属化合物(TiC，ZrN)。其普适关系式为：log[p&lt；min&gt；/Z^3]=-5.29log[1.01+0.285x2(Z/n)r&lt；min&gt；]式中，Z是元素的原子序数，n是主量子数。这种关系为我们从根本上理解物质中化学键的性质提供了线索。

Knowledge of spatial electron density distribution, p(r), is so fundamental for the full understanding of the nature of the chemical bond between atoms in matter. For convenience, several methods have been proposed for analyzing p(r). For example, following the Mulliken population analysis method, overlap populations and orbital populations are calculated and used as a measure of chemical interactions between atoms. Such interactions may be also characterized by the Laplacian of the electron density, ▽^2 p(r). However, despite great efforts, there has been little information of the feature of p(r) common to every matter. Here, we show a universal relation between electron density minima, p_<min> and atomic or ionic radii, r_<min>, which was discovered from the first principles DV-Xα molecular orbital calculations of electronic structures in matter over 150 species, including gasses(H_2,O_2), water(H_2O), diamond(C), metals(Fe,Al), semi-conductors(Si,Ge), oxides(MgO,Al_2O_3,SiO_2,BaTiO_3), alkali halide crystals (NaCl,KCl), and metal compounds (TiC,ZrN). The universal relation was expressed as,log[p_<min>/Z^3]=-5.29 log[1.01+0.285x 2(Z/n)r_<min>].Here, Z is the atomic number of element and n is a principal quantum number. This relation provides us a clue to the understanding of the nature of chemical bond in matter in a fundamental manner.