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

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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.