Cu_3O_(12)^(17-)模型簇的电子态

ELECTRONIC STATES OF THE Cu_3O_(12)^(17-) MODEL CLUSTER

在铜氧基超导体中,超导电性与接近充满的Cu3d-O2p价带空穴浓度有关.若干研究表明,添加空穴进入CuO_2面σ(P_(x,y))轨道,但另外一些工作认为,空穴态存在于Cu-O面π(p_(x,y))或π(p_z)轨道,还有其它一些作者建议,空穴集居于BaO面上σ(p_z)轨道.通过理论计算来区分未占O2p态的特征具有重要意义.因此,本文对模型簇Cu_3O_(12)^(17-)进行了Fenske-Hall MO计算,探讨了添加空穴态的对称性和添加对Cu-O键强度的影响.

The Fenske-Hall molecular orbital calculations were performed on the modelcluster Cu_3O_(12)^(17-). The calculated results revealed that the valence levels are mainlycomposed of Cu d and O p components, and the levels near E_f are predominately ofO p nature. Oxidation removes the antibonding electrons from the Cu (1) d_(z^2-y^2) MOand strengthens the chain Cu (1) --O (1) and Cu (1) --O (4) bonds so that they haveslightly larger overlap population than the plane Cu (2) --O (2) and Cu(2) --O(3)bonds. The oxidation beyond the Cu^(2+) state does not lead to Cu^(3+) but to O^- state sothat the O(1) as well as O(4) ions have slightly smaller electron charge than theO(2) and O(3) ions. The holes introduced by doping reside primarily on the Cu--Ochain with dominantly sigma O (4) 2P_z character.