Theory of electrochemical effects in alloys

Abstract

We present a theory of electron charge transfer and electrochemical effects in alloys of simple metals, based on the Hohenberg—Kohn density variational principle for an inhomogeneous electron gas. This approach has the advantage that we may imagine constructing a heterovalent alloy dlrectly from the electrically neutral Wigner—Seitz cells of the parent metals, Instead of using a uniform electron gas as a starting approximation. The energy functional derivative which occurs in the Hohenberg—Kohn theory may be interpreted as a local Fermi level or chemical potential which governs the transfer of charge between different alloy atomic cells. Calculations show an approximate correlation between the Fermi level in an atomic cell and the Pauling electronegativity of that particular atom. We show that the energy released by charge transfer is proportional to the square of the Fermi level or electro-negativity difference between different cells, in agreement with the commonly accepted expression due to Pauling. Our theory may also be used to study the problem of mismatch of electron density at the boundaries between different alloy cells. We have used it to calculate various contributions to the heats of formation of a series of simple metal alloys.