GROUND-STATE PROPERTIES OF CDXSN1-XTE - THE ROLE OF D-ELECTRONS

Within the framework of density functional theory (DFT), we calculate the ground-state electronic properties of CdxSn1-xTe using norm-conserving pseudopotentials in connection with the local density (LDA) and virtual crystal approximation (VCA). Our particular interest is in the influence of the Cd-4d and the Sn-4d electrons by comparing results obtained with pseudopotentials, which either consider the d-electrons explicitly or in the frozen core. In the mixed crystal system CdxSn1-xTe, the transition from a ten- (x = 0) to an eight-electron (x = 1) system is realized, which is accompanied by a change of the crystal structure from rock salt (SnTe) to zinc blende (CdTe). By calculating the ground-state energies, we find the equilibrium lattice constants as the function of x and the bulk modulus, as well as the crossover value of x for the transition from rock-salt to zinc blende. The calculated lattice constants and bulk moduli are in much closer agreement with experimental data if the d-electrons are taken into account explicitly, whereas the crossover is rather insensitive with respect to the d-electrons. In view of the electronic charge density, we demonstrate the decrease of ionicity for increasing x. (C) 1994 John Wiley & Sons, Inc.