A THEORETICAL INVESTIGATION OF THE ELECTRONIC-STRUCTURE, HYPERFINE PROPERTIES AND BINDING-ENERGIES OF MUONIUM CENTERS IN CUPROUS CHLORIDE

A series of self-consistent local-spin-density molecular-cluster calculations has been performed to investigate the electronic structure, the hyperfine (hf) properties and binding energies of muonium centres in cuptous chloride. Spin-polarization was taken into account on a finite, stoichiometric cluster including Cu7Cl7 and an interstitial muonium (Mu) atom. Different Mu positions along the direction <111> of the CuCl zinc blende structure between the two inequivalent tetrahedral interstitial sites (hereafter T(cu) and T(ca)) were investigated. Our results indicate a localization of Mu close to the T(cu) site, shifted about 0.5 angstrom toward the apical Cu atom of the employed cluster. Such a fact nicely agrees with experimental findings and it has been discussed and rationalized on the basis of the different bonding interaction between Mu and the nearest neighbours. In the light of our theoretical outcomes, the single-electron model proposed by Cox and Symons for the reduction of the Fermi contact term A of the hf coupling constant in I-VII semiconductors seems to be rather inadequate. The accord between experimental and theoretical hyperfine parameters is satisfactory. In particular, theoretical data would indicate that the two different muonium centres, experimentally detected in CuCl, have the same chemical environment. These results are encouraging for the study of other compound semiconductors.