对“SrRu $_{1-x}$ Ti $_x$ O $_3$的电子结构和轨道有序：GGA +U研究”的评论
Comment on "Electronic structure and orbital ordering of SrRu$_{1-x}$Ti$_x$O$_3$: GGA+U investigations"
摘要：
在论文PRB { \bf 77}，085118（2008）中，作者得出结论，在局部密度近似的限制内，在SrRu $_{1-x}$ Ti $_x$ O $_3$中Ti掺杂诱导的半金属性的观察是无效的，因为实验结果表明绝缘行为。据描述，在该系统中观察到的x = 0.5处的金属-绝缘体转变（MIT）是由于Ti取代x后现场库仑排斥强度U的增强而出现的。MIT主要取决于U，部分取决于x和/或无序。所有这些结论都与实验观测结果形成鲜明对比，实验观测结果预测Anderson绝缘相在x = 0.5（费米能级的有限局域态密度）。由于电子关联导致的硬能隙出现在高得多的x（~ 0.8）处。此外，已充分确定，同价取代对原位$U$（局部变量）的影响可忽略不计。这些不一致的出现是由于这样一个事实，即代表体电子结构的计算结果相比，占主导地位的表面贡献的实验结果。在文献中已经得到的实验体谱显示出在费米能级上的有限态密度，即使对于x >= 0.5的样品，这表明早期研究中的半金属相的结论是合理的。因此，在这些系统中，绝缘体到金属的转变是由带宽，W而不是U驱动的，并且无序在金属-绝缘体转变中起主导作用。人们需要考虑体光谱来数值地再现体电子结构。
英文摘要：
In the paper, PRB {\bf 77}, 085118 (2008), the authors conclude that the observation of Ti-doping induced half-metallicity in SrRu$_{1-x}$TI$_x$O$_3$ within the limit of local density approximations is not valid as the experimental results indicate insulating behavior. It was described that the metal-insulator transition (MIT) at x = 0.5 observed in this system appears due to the enhancement of on-site Coulomb repulsion strength, U with Ti substitutions, x. The MIT primarily depends on U and partially on x and/or disorder. All these conclusions are in sharp contrast to the experimental observations, which predicted Anderson insulating phase at x = 0.5 (finite localized density of states at the Fermi level). The hard gap due to electron correlation appears at much higher x (~ 0.8). In addition, it is well established that homovalent substitution has negligible influence on on-site $U$ (a local variable). These inconsistencies appear due to the fact that the calculated results representing the bulk electronic structure are compared with the experimental results dominated by surface contributions. The experimental bulk spectra, already available in the literature exhibit finite density of states at the Fermi level even for x >= 0.5 sample, which suggests that the conclusion of half metallic phase in an earlier study is reasonable. Thus, the insulator to metal transition in these systems is driven by bandwidth, W rather than U and disorder plays dominant role in the metal-insulator transition. One needs to consider the bulk spectra to reproduce numerically the bulk electronic structure.
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