DFT+DMFT study of oxygen vacancies in a Mott insulator

Oxygen vacancies are a common source of excess electrons in complex oxides. In Mott insulators, these additional electrons can induce a metal-insulator transition (MIT), fundamentally altering the electronic properties of the system. Here we study the effect of oxygen vacancies in LaTiO3, a prototypical Mott insulator close to the MIT. We show that the introduction of oxygen vacancies creates a vacancy-related band immediately below the partially filled Ti-t 2g bands. We study the effect of this additional band on the Mott MIT using a combination of density functional theory and dynamical mean-field theory (DFT+DMFT), employing a minimal correlated subspace consisting of effective Ti-t 2g orbitals plus an additional Wannier function centered on the vacancy site. We find that the Mott insulating state in LaTiO3 is robust to the presence of the vacancy band, which remains fully occupied even in the presence of a local Coulomb repulsion, and therefore does not cause a doping of the Mott insulator

氧空位是复杂氧化物中过剩电子的常见来源。在莫特绝缘体（Mott insulators）中，这些额外电子可诱导金属-绝缘体转变（metal-insulator transition, MIT），从根本上改变体系的电子性质。本文以接近金属-绝缘体转变的典型莫特绝缘体钛酸镧（LaTiO₃）为研究对象，探讨氧空位的影响。研究发现，氧空位的引入会在部分填充的Ti-t₂g能带正下方形成一条与空位相关的能带。我们结合密度泛函理论（density functional theory, DFT）与动力学平均场理论（dynamical mean-field theory, DMFT），采用由有效Ti-t₂g轨道以及空位位点中心处的额外瓦尼尔函数（Wannier function）构成的最小关联子空间，研究了该额外能带对莫特金属-绝缘体转变的影响。结果表明，钛酸镧中的莫特绝缘态对空位能带具有鲁棒性：即便存在局域库仑排斥，空位能带仍保持完全占据，因此不会对该莫特绝缘体产生掺杂效应。