First-principles study of defect-induced potentials in Ca2CUO2Cl2
First-principles study of defect-induced potentials in Ca2CUO2Cl2
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DOI：
10.1103/physrevb.80.085120
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发表时间：
2009-08
影响因子：
3.7
通讯作者：
Y. Kumagai;F. Oba;I. Yamada;M. Azuma;I. Tanaka
中科院分区：
文献类型：
--
作者：
Y. Kumagai;F. Oba;I. Yamada;M. Azuma;I. Tanaka
用$\TEXT{GGA}+U$方法研究了${\text{Ca}}_{2}{\text{CuO}}_{2}{\text{Cl}}_{2}$中Na、K杂质和Ca位空位({\Text{Na}}_{\Text{Ca}}，${\Text{K}_{\Text{Ca}}和${\Text{V}}_{\Text{Ca}})的局域原子和电子结构及其诱导静电势.研究发现，${\Text{Na}_{\Text{Ca}}$和${\Text{K}}_{\Text{Ca}}$从原来的Ca位向氯平面明显松弛。当存在${\Text{V}}_{\Text{Ca}}$时，其邻近的Ca接近空位，而Cl和O向外松弛。通过对铜位和氧位的局部静电势的分析，我们发现${\Text{Na}_{\Text{Ca}}$诱导的电势与${\Text{K}_{\Text{Ca}}$的诱导电势几乎相同，而${\Text{V}_{\Text{Ca}}的诱导电势大约是它的两倍。缺陷感生电势由介电介质下的点电荷模拟。发现原子弛豫使有效介电常数增加了近三倍，表明了原子弛豫对势垒屏蔽的重要性。由总能量差得到的小极化子的稳定能接近势能。这些结果表明，在缺陷诱导的静电势下，极化子与缺陷之间的相互作用可以用极化子的正电荷来很好地描述。
The local atomic and electronic structures of the Na and K impurities and the vacancy at the Ca site (${\text{Na}}_{\text{Ca}}$, ${\text{K}}_{\text{Ca}}$, and ${\text{V}}_{\text{Ca}}$), and their induced electrostatic potentials in ${\text{Ca}}_{2}{\text{CuO}}_{2}{\text{Cl}}_{2}$ have been investigated by using the $\text{GGA}+U$ approach. It is found that ${\text{Na}}_{\text{Ca}}$ and ${\text{K}}_{\text{Ca}}$ are markedly relaxed toward the Cl plane from the original Ca site. When ${\text{V}}_{\text{Ca}}$ 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 ${\text{Na}}_{\text{Ca}}$-induced potential is almost the same as the ${\text{K}}_{\text{Ca}}$-induced potential, and the ${\text{V}}_{\text{Ca}}$-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.