Charge-density analysis of GaS

Abstract

The electron density in the ${A}^{\mathrm{III}}{B}^{\mathrm{VI}}$ crystal GaS was experimentally determined by x-ray diffraction. The resulting density distribution varies markedly from the distribution predicted by the pseudopotential model proposed by Schl\"uter et al. The real bonds observed in the x-ray diffraction determined distribution are curved and are located not only between Ga-Ga and Ga-S nearest neighbors as predicted by the pseudopotential model, but also between Ga and S next-nearest neighbors in the same elementary cell, between Ga and S atoms in adjoining elementary cells, and between S-S interlayer neighbors in the same elementary cell. The two atoms Ga and S are highly polarized. These findings allow a better understanding of the bondings and the discrepancies between our experimental findings, and the present pseudopotential model should permit an improvement in a future theoretical model for bonding in the ${A}^{\mathrm{III}}{B}^{\mathrm{VI}}$ crystals.