A thermochemical scheme containing two adjustable variables per element has been developed by Miedema and co-workers which correctly predicts the signs of the heats of formation of 500 binary metallic alloys. Here we propose a simple but $l$-dependent orbital quantum model based on the valence energies of hydrogenic ions which contains no adjustable elemental variables and which fits the Miedema variables for 25 simple metals with an rms accuracy of 3%.

• Received 21 July 1977

DOI:https://doi.org/10.1103/PhysRevLett.39.1687