First-principles study on the multiplet structures of CuO5 pyramid in Bi2Sr2CaCu2O8+delta

In this paper we investigate the multiplet structure of a single CuO5 pyram id embedded in Bi2Sr2CaCu2O8+delta (Bi2212) for an insulating phase of delt a = 0 and a superconducting phase of delta = O with T-c = 85 K. In this stu dy, we use the multi-configuration self-consistent field variational method with configuration interaction to calculate the lowest states of the Zhang -Rice spin-singlet ((1)A(1)) and Hund's coupling spin-triplet (B-3(1)) as a ccurate as possible. In the case of delta = O we find that the 'Al state is the lowest. It is lower than the B-3(1) state by 2.15 eV. On the other han d, in the case of delta = 0.25 we find that the (1)A(1) and the B-3(1) mult iplets are very close in energy; and mixed easily by transfer interaction b etween clusters. In the case of delta = 0.25, we show that a coherent state for a dopant hole is composed in such a way that the (1)A(1) and the B-3(1 ) multiplets appear alternately when the localized spin form local antiferr omagnetic ordering in a region of the spin-correlation length.