The energetic stability,the structural and the electronic properties of rhombohedral and tetragonal PbZr_(0.5)Ti_(0.5)O_2 are systematically investigated by the first-principles plane-wave pseudopotential and the virtual crystal approximation(VCA) based on the density functional theory,within the frameworks of local density approximation(LDA) and generalized gradient approximation(GGA).Our calculation results show that the total energy of the rhombohedral phase is lower than that of the tetragonal phase,whi...