Department of Chemistry and Biochemistry, Materials Department and Materials Research Laboratory, University of California, Santa Barbara, CA 93106, USA.
J Phys Condens Matter. 2011 Nov 23;23(46):465501. doi: 10.1088/0953-8984/23/46/465501. Epub 2011 Nov 1.
PbPdO₂, a ternary compound containing the lone pair active ion Pb²⁺ and the square planar d⁸Pd²⁺ ion, has attracted recent interest because of the suggestion that its electronic structure, calculated within density functional theory using either the local density or the generalized gradient approximation, displays zero-gap behavior. In light of the potential ease of doping magnetic ions in this structure, it has been suggested that the introduction of spin, in conjunction with zero band gap, can result in unusual magnetic ground states and unusual magnetotransport. It is known that most electronic structure calculations do not properly obtain a band gap even for the simple oxide PdO, and instead obtain a metal or a zero-gap semiconductor. Here we present density functional calculations employing a screened hybrid functional which correctly obtain a band gap for the electronic structure of PdO. When employed to calculate the electronic ground state of PbPdO₂, a band gap is again obtained, which is consistent with both the experimental data on this compound, as well as a consideration of valence states and of metal-oxygen connectivity in the crystal structure. We also present comparisons of the absolute positions (relative to the vacuum level) of the conduction band minima and the valence band maxima in α-PbO, PdO and PbPdO₂, which suggest ease of p-type doping in PbPdO₂, that has been observed even in nominally pure materials.
PbPdO₂ 是一种含有孤对活性离子 Pb²⁺和平面正方形 d⁸Pd²⁺离子的三元化合物，由于其电子结构在密度泛函理论下计算时，无论是使用局域密度近似还是广义梯度近似，都显示出零带隙行为，因此最近引起了人们的兴趣。鉴于在这种结构中容易掺杂磁性离子，有人提出，引入自旋和零带隙可以导致异常的磁基态和异常的磁输运。众所周知，大多数电子结构计算即使对于简单的氧化物 PdO 也不能正确获得带隙，而是得到金属或零带隙半导体。在这里，我们提出了一种使用屏蔽杂化泛函的密度泛函计算，该方法可以正确获得 PdO 电子结构的带隙。当用于计算 PbPdO₂ 的电子基态时，再次得到了一个带隙，这与该化合物的实验数据以及对晶体结构中价态和金属-氧连接性的考虑是一致的。我们还比较了 α-PbO、PdO 和 PbPdO₂ 中导带最小值和价带最大值的绝对位置（相对于真空能级），这表明即使在名义上纯净的材料中，PbPdO₂ 也容易进行 p 型掺杂，这一点已经得到了观察。
