First-principles study of defect-induced potentials in Ca2CuO2Cl2

Abstract

The local atomic and electronic structures of the Na and K impurities and the vacancy at the Ca site (NaCa, KCa, and VCa), and their induced electrostatic potentials in Ca2 CuO2 Cl2 have been investigated by using the GGA+U approach. It is found that NaCa and KCa are markedly relaxed toward the Cl plane from the original Ca site. When VCa exists, its neighboring Ca approaches the vacancy site, and Cl and O are relaxed outwardly. From the analyses of the local electrostatic potentials at the Cu and O sites, we found that the NaCa -induced potential is almost the same as the KCa -induced potential, and the VCa -induced potential is about twice as large. The defect-induced potentials are modeled by point charges under a dielectric medium. The atomic relaxation is found to increase the effective dielectric constants approximately threefold, indicating the importance of its contribution to the screening of the potential. The stabilization energies of small polarons obtained by the total energy differences are close to the potential energies. These results suggest that the interaction between the polaron and defects is well described by a positive charge of the polaron under the defect-induced electrostatic potential.