Bond ionicities in CuBC2 chalcogenides (B = Al, Ga, In; C=S, Se, Te)

The bond ionicities, f(i,Cu-C) and f(i,BC) of several CuBC2 (B=Al, Ga, In, and C=S, Se, Te) chalcopyrite compounds are estimated by means of the Phill ips-Van Vechten dielectric theory for binary tetrahedral compounds and Levi ne's extension to multibond crystals in the same way as Neumann [Crystal Re s. Technol. 18, 1299 (1983)]. The influence of Cu 3d electrons has been tak en into account considering Jaffe-Zunger [Phys. Rev. B 29, 1882 (1984)] ban d-structure calculations in chalcopyrite compounds, and performing a simple extrapolation for Te compounds. The Cu-C bond susceptibilities have been e stimated from the static dielectric constant values obtained by Marquez and Rincon [Phys. Status Solidi B 191, 115 (1995)], and a set of Cu-C bond sus ceptibilities is proposed. The evaluated f(i,Cu-C) bond ionicities were fou nd to increase with the atomic fractional coordinate of the C atom, x[anion ], indicating that the anion position is a good estimation of the Cu-C bond ionicity.