Brown Joshua J, Page Alister J
School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia.
J Chem Phys. 2021 Mar 28;154(12):124121. doi: 10.1063/5.0045526.
We investigate how the Hubbard U correction influences vacancy defect migration barriers in transition metal oxide semiconductors. We show that, depending on the occupation of the transition metal d orbitals, the Hubbard U correction can cause severe instabilities in the migration barrier energies predicted using generalized gradient approximation density functional theory (GGA DFT). For the d oxide SrTiO, applying a Hubbard correction to the Ti 3d orbitals below 4-5 eV yields a migration barrier of ∼0.4 eV. However, above this threshold, the barrier increases suddenly to ∼2 eV. This sudden increase in the transition state barrier arises from the Hubbard U correction changing the Ti t/e orbital occupation, and hence electron density localization, along the migration pathway. Similar results are observed in the d oxide ZnO; however, significantly larger Hubbard U corrections must be applied to the Zn 3d orbitals for the same instability to be observed. These results highlight important limitations to the application of the Hubbard U correction when modeling reactive pathways in solid state materials using GGA DFT.
我们研究了哈伯德U校正如何影响过渡金属氧化物半导体中的空位缺陷迁移势垒。我们表明，根据过渡金属d轨道的占据情况，哈伯德U校正会导致使用广义梯度近似密度泛函理论（GGA DFT）预测的迁移势垒能量出现严重不稳定。对于d氧化物SrTiO，对低于4 - 5 eV的Ti 3d轨道应用哈伯德校正会产生约0.4 eV的迁移势垒。然而，高于此阈值时，势垒会突然增加到约2 eV。过渡态势垒的这种突然增加源于哈伯德U校正改变了沿迁移路径的Ti t/e轨道占据情况，进而改变了电子密度局域化。在d氧化物ZnO中也观察到了类似结果；然而，对于Zn 3d轨道，必须应用明显更大的哈伯德U校正才能观察到相同的不稳定性。这些结果突出了在使用GGA DFT对固态材料中的反应路径进行建模时应用哈伯德U校正的重要局限性。
