MICROSCOPIC SCREENING AND PHONON-DISPERSION IN GERMANIUM

This paper shows results for the phonon dispersion of Ge in an extreme-tight-binding calculation for different values of the ionic-pseudopotential parameters. It is found that in this model meaningful results, comparable to experiment, can be obtained for the macroscopic dielectric function but not for phonon frequencies, in contradiction with a claim made in a paper by Arya and Jha. Similar results are obtained for C and Si. This indicates that the extreme-tight-binding band model is too simple to be useful in phonondispersion calculations. The present authors have shown elsewhere that the inclusion of the higher bands and the consistency between electron-ion and crystal pseudopotential play an essential role in obtaining meaningful phonon frequencies for semiconductors. © 1979 The American Physical Society.