Electronic properties of simple metals, electronegativity scales and alloy formation

Abstract

The conduction electrons of a metal are described by a standard simple expression for the total energy of a constituent atomic cell, which includes electrostatic and correlation effects as well as the interaction with the central ion through a model potential with an empty core of radius R c. The effect of the ion potential on the shape of the effective free electron band is assumed to be represented by an effective mass parameter m ∗ and additional band structure effects are ignored. While the use of constant core potentials is incompatible with the usual virial theorem, we show that one may determine m ∗ and a non-zero R c by imposing the zero-pressure condition together with a weaker form of the virial theorem, the so-called electronegativity virial theorem. This renders the total energy negative for all electron densities, unlike in the case of jellium which is energetically unstable at high densities. Our values for R c are in good agreement with those determined by Ashcroft. The effective masses m ∗ are close to Ham's band structure masses for alkali metals, and to experimental specific heat masses for some polyvalent materials. Detailed results for binding energies of simple metals are in good agreement with experimental data, but the agreement is less satisfactory in the case of the bulk modulus. An electronegativity parameter χ is defined and found from our model to have a universal behavior proportional to the inverse atomic cell radius. Two somewhat different electronegativity scales are obtained depending on whether atomic volumes or binding energies are used as input data in the expression for χ. These parameter free scales correlate surprisingly well with both Miedema's and Pauling's empirical electronegativity scales for simple metals. The comparison of our electronegativity scales with other theoretical scales and their application to the calculation of the charge term in the heat of formation of low transfer alloys are also briefly discussed.