A simple formula involving the geometric mean of the electronegativities of the two components is proposed for the determination of the Fermi energies and hence the photoelectric thresholds of simple binary compounds, and is found to be surprisingly accurate for all presently available data. A theoretical basis for the use of the "postulate of the geometric mean" is also given.

• Received 8 April 1974

DOI:https://doi.org/10.1103/PhysRevLett.33.1088