The electronic structure of strongly correlated electrons at the surface of transition-metal oxides

在局域密度近似(LDA)和动力学平均场理论(DMFT)的基础上，用第一性原理方法研究了过渡金属氧化物表面强关联电子的电子结构。在DMFT计算中，用Hirsch和Fye的量子蒙特卡罗方法求解了单Anderson杂质问题。我们主要研究了最近进行光电子能谱测量的立方钙钛矿型SrVO_3的(001)面，由于SrVO_3的表面结构尚不清楚，我们首先考虑了其具有SRO层和VO_2层端面的理想解理表面。我们使用了FLAPW总能量代码(FLEUR)来确定表面原子在法向的驰豫。研究发现，围绕中心V原子构成八面体的O原子的位移很小。对于所有的结构，我们用嵌入的格林函数方法确定了半无限表面的LDA电子结构。然后，将计算的态密度(DOS)投影到最外层的V原子的2g&gt；轨道上，作为后续DMFT计算的输入.对于SRO层终止表面，最外层V原子法向配位数的减少导致d&lt；Xz/Yz&gt；带的LDA态密度显著变窄，这导致计算的表面准粒子谱中的关联特征强于体相.在VO2层终止表面的情况下，最外层V位的局域八面体对称性的缺乏导致了V原子价电子结构的实质性变化，并导致了与体相相比t&lt；2g&gt；价电荷的相当大的重排。关联效应进一步促进了这三个t&lt；2g&gt；轨道之间的电荷转移。

We have investigated the electronic structure of strongly correlated electrons at the surface of transition-metal oxides by a first principles method within the local density approximation (LDA) plus dynamical mean-field theory (DMFT). In the DMFT calculation, the single Anderson impurity problem was solved using the quantum Monte Carlo technique of Hirsch and Fye. We focused on the (001) surfaces of cubic perovskite SrVO_3 for which photoemission measurements were performed recently.As the surface structure of SrVO_3 is not known, we first considered its ideal cleaved surfaces with both SrO-layer and VO_2-layer terminations. We used the FLAPW total energy code (FLEUR) to determine the relaxations of surface atoms in the normal direction. It was found that the displacements of the O atoms that constitute octahedrons surrounding central V atoms are rather small. For all the structures, we determined the LDA electronic structure of semi-infinite surfaces using the embedded Green function method. Then, the calculated density of states (DOS) projected on the t_<2g> orbitals of an outermost V atom was used as an input to the subsequent DMFT calculations.For the SrO-layer terminated surfaces, the reduced coordination number of outermost V atoms in the normal direction gives rise to a significant narrowing of the LDA DOS for the d_<xz/yz> bands, which leads to stronger correlation features in the calculated surface quasi-particle spectra than in the bulk. In the case of VO2-layer terminated surfaces, the lack of the local octahedral symmetry at outermost V sites causes substantial changes in the valence electronic structure of the V atoms and results in a considerable rearrangement of t_<2g> valence charge compared to the bulk. This charge transfer among the three t_<2g> orbitals is further promoted by correlation effects.