Abstract
In order to find the most stable distribution of hole carriers, the bond-valence-sum (BVS) and the electrostatic energy for a composite crystal Ca13.6Sr0.4Cu24+yO41+z (y=-0.017 and z=-0.035) were calculated using modulated structure data at ambient pressure and room temperature. The BVS calculation suggests that at least four holes per molecule stay in the 1-D chain. The lowest Madelung energy was given from a hole distribution in which all of the self doped holes occupy the sites in the 1-D chain. However, transfer of one hole to the ladder per molecule costs only about 0.7, eV/mol. Considering experimental uncertainties in the structural parameters or contribution of other terms such as kinetic energy to the total energy, it is implied that a small number of holes can be transferred into the ladder. In the 1-D chain, the hole tend to be localized in every other copper site or its adjacent oxygen sites by the structural modulation reflecting the Coulomb interaction between them.
