Effective interatomic potentials in strong-scattering open shell metals: application to bonding force in d-band metals

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Abstract
A method for the calculation of an open shell, strong-scattering metal cohesive energy Ecoh in terms of the effective interaction is presented. It involves a so called reference medium defined as an ensemble of weighted atomic configurations which are significant for the problem under consideration. Ecoh is written as a sum of n-body interactions up to n=M plus a residual error epsilon M. The effective forces are determined in a unique way by making epsilon M statistically small for the reference medium configurations. The M=2 (up to pair-force) description is studied in detail for the bulk, weak defect case. A metal, liquid-like reference medium is then appropriate and the recently developed liquid metal theory is used to derive closed equations for the effective pair interaction within the Kohn-Sham local density approximation. The theory is applied to the study of d-bonding pair interaction in transition metals as a function of interatomic distance R and of d-band charge Zd, within Andersen's tight-binding atomic sphere approximation. The pair interaction is found to be mainly attractive and to behave as Zd(10-Zd)/R10 when R is near the physical hard-core diameter. The behaviour is more complicated when R is much larger and is explained with the help of an approximate solution of the full equations. Finally the Dick-Overhauser overlap pair interaction, which is valid for closed shell atoms, is extended to the open-shell case.