School of Physical Sciences, National Institute of Science Education and Research, P.O.: Sainik School, Bhubaneswar-751005, India.
Phys Chem Chem Phys. 2010 Feb 21;12(7):1564-70. doi: 10.1039/b918890h. Epub 2010 Jan 12.
Most d(0) transition metal (TM) oxides exhibit anomalously large Born dynamical charges associated with off-centering or motion of atoms along the TM-O chains. To understand their chemical origin, we introduce "Wannier orbital overlap population" (WOOP) and "Wannier orbital position population" (WOPP) in terms of the Wannier function based description of electronic structure obtained within first-principles density functional theory. We apply these concepts in a precise analysis of anomalous dynamical charges in PbTiO(3), BaTiO(3) and BaZrO(3) in the cubic perovskite structure. Determining contributions of different atomic orbitals to the dynamical charge and their break-up into local polarizability, charge transfer and covalency, we find that p orbitals of oxygen perpendicular to the -TM-O- chain contribute most prominently to the anomalous charge, by facilitating a transfer of tiny electronic charge through one unit cell from one TM atom to the next. Our results explain why the corner-shared linkage of TMO(6) octahedra, as in the perovskite structure, is ideal for large dynamical charges and hence for ferroelectricity.
大多数 d0 过渡金属 (TM) 氧化物表现出异常大的 Born 动力学电荷，这与原子沿 TM-O 链的偏移或运动有关。为了理解其化学起源，我们在第一性原理密度泛函理论中基于电子结构的 Wannier 函数描述引入了“Wannier 轨道重叠人口”（WOOP）和“Wannier 轨道位置人口”（WOPP）。我们将这些概念应用于对立方钙钛矿结构中的 PbTiO3、BaTiO3 和 BaZrO3 中异常动力学电荷的精确分析。确定不同原子轨道对动力学电荷的贡献及其分解为局部极化率、电荷转移和共价性，我们发现垂直于 -TM-O-链的氧的 p 轨道对异常电荷的贡献最为显著，因为它通过在一个单元中从一个 TM 原子到下一个 TM 原子转移微小的电子电荷来促进这一过程。我们的结果解释了为什么 TMO6 八面体的角共享连接，如钙钛矿结构，是大动力学电荷的理想选择，因此也是铁电性的理想选择。
