Theory of energy bands and related properties of 4d transition metals. III. s and d contributions to the equation of state

Abstract

For pt.II see ibid., vol.7, p.1009 (1978). The s and d contributions to the pressure and bulk modulus across the series and as a function of volume are presented using Pettifor's partial pressure expression and the results of part I of this series on the behaviour of the energy bands. It is shown that whereas Friedel's d bond contribution is primarily responsible for the cohesive energy, the s electrons are crucial for providing the repulsive pressure to counter the attractive d contribution at the equilibrium atomic volume. Moreover, because of ion core orthogonality constraints, the s electrons determine the bulk modulus away from the noble metal end of the series. The hybridisation contribution is included by assuming it to be proportional to the d resonant width. The cohesive energy is predicted to better than about 10%, the equilibrium atomic volume to 25%, and the bulk modulus (excluding Pd and Ag) to better than 20% across the 4d series. The importance of the neglected second-order contributions such as three-centre integrals is demonstrated.