New Concepts of Metallic Bonding

Author: McAdon, Mark Herbert

Year: 1988

Degree: Dissertation (Ph.D.)

Advisor: Goddard, William A., III

Committee Members: Beauchamp, Jesse L.; Goddard, William A., III; Gray, Harry B.; Cross, Michael Clifford

Option: Chemistry

DOI: 10.7907/jtpr-6m88

Abstract

This thesis presents results derived from ab initio wavefunctions, leading to new concepts of metallic bonding — real-space concepts that do not require "thinking in reciprical (k) space." As the first step in this study of metallic bonding, Hartree-Fock and generalized valence bond wavefunctions are presented for ring clusters composed of monovalent atoms (Cu, Ag, Au, Li, and Na). These results show that one-dimensional metals need not exhibit Peierls instabilities, charge density waves, or spin density waves. In addition, magnon spectra calculated using various wavefunctions are compared with each other and with magnon spectia obtained with simple nearest-neighbor Ising and Heisenberg hamiltonians.

Generalized valence bond wavefunctions for small metal clusters lead to the conclusion that, for metallic systems, the valence electrons occupy interstitial regions — bond midpoints for one-dimensional systems, triangular hollows for two-dimensional systems, and tetrahedral hollows for three-dimensional systems. The new concepts of metallic bonding are summarized by a set of rules for the valence sp electrons of metallic systems. These rules are used to derive the low-lying isomers of small metal clusters, and are expected to prove useful in predicting the chemistry and catalytic properties of such systems. Applying these rules to bulk metals leads to a new explanation of the solubility limits governing alloys of monovalent, divalent, trivalent, and tetravalent atoms. These rules are expected to prove valuable in describing the localized states in metals and alloys such as defects or interfaces.

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