Ground‐state properties of Cd x Sn 1– x Te: The role of d ‐electrons

Within the framework of density functional theory ( DFT ), we calculate the ground‐state electronic properties of Cd x Sn 1– x Te 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‐4 d and the Sn‐4 d electrons by comparing results obtained with pseudopotentials, which either consider the d ‐electrons explicitly or in the frozen core.In the mixed crystal system Cd x Sn 1– x Te, 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 constant 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 . © 1994 John Wiley & Sons, Inc.