PNNL

Abstract

Connections established during the 20th century between bond length, radii, bond strength, bond valence and crystal and molecular chemistry are briefly reviewed followed with a survey of the physical properties of the electron density distributions for a variety of minerals and representative molecules, recently generated with first-principles local density based quantum mechanical methods. The structures for several minerals, geometry-optimized at ambient conditions and at a variety of pressures, match those determined experimentally within several percent. The structures and the physical properties of model experimental electron density distributions determined with high resolution and high energy synchrotron single crystal X-ray diffraction data also closely match those calculated with first principles methods. As the electron density is progressively accumulated and locally concentrated between pairs of bonded atoms, the nuclei are progressively shielded and the bond lengths and the bonded radii of the atoms decrease. Concomitant with the decrease in bond length, the local kinetic density energy increases while the potential energy and the electronic energy densities both decrease for intermediate and shared interactions with the potential energy dominating the local energy for the shorter bonded interactions. The shorter the bonds, the more negative the local electronic energy density, the greater the stabilization and the greater the shared character of the bonded interactions.