Properties of Atoms in Molecules: Atoms Forming Molecules

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This paper studies the evolution of the electron densities of two separated atoms into an equilibrium molecular distribution. A range of interactions is considered: from closed-shell with and without charge transfer, through polar-shared, to equally shared interactions. The changes in the density are monitored in terms of the properties of the density at the bond critical point and the shape of the interatomic surface. The effect of these changes on the properties of the atoms defined as proper open systems is determined. The “harpoon mechanism” operative in the formation of LiF is found to exert dramatic effects on the electron density and on the atomic and molecular properties. The virial and the Ehrenfest force theorems in their molecular, atomic, and local forms, together with the Hellmann−Feynman theorem, provide an understanding of the similarities and differences in the bonding resulting from closed-shell, shared, and polar interactions. The effect of the long-range dispersion forces on the electr...