We present the phonon spectrum of TiOCl computed using hybrid density functional theory (DFT). A complete analysis of the spectrum is performed for the space group Pmmn (high symmetry phase) and the space group P2_1/m (low symmetry phase), which is the symmetry of the spin-Peierls phase. We show that the nonlocal correlations present in the hybrid DFT approach are important for understanding the electron-lattice interactions in TiOCl. The computed frequencies compare well with those observed in Raman and infrared spectroscopy experiments and we identify the origin of an anomalous phonon observed in Raman spectroscopy. The relationship between relevant zone boundary phonons in the high symmetry phase and the zone center counterparts in the P2_1/m symmetry allow us to speculate about the origin of the spin-Peierls phonon.
Giant phonon anomalies in the pseudo-gap phase of TiOCl
本文报道了自旋为1/2的量子磁体TiOCl的红外和拉曼光谱结果。在声子谱的温度依赖性中发现了巨大的异常，这暗示了电子自由度与晶格的不寻常耦合。这些异常发展在一个广泛的温度间隔，这表明存在一个扩展的波动制度。这定义了一个伪能隙相，其特征在于局部自旋能隙。在100 K以下，维度交叉导致二聚基态，自旋能隙约为2 $Δ_{spin}\approx$ ~430 K.
Spectroscopic and first principle DFT+eDMFT study of complex structural, electronic, and vibrational properties of $M_2$Mo$_3$O$_8$ ($M$=Fe, Mn) polar magnets
采用光谱、X射线衍射、密度泛函理论（DFT）和密度泛函理论+嵌入动力学平均场（DFT+eDMFT）方法研究了六方结构$M_2$ Mo $_3$ O $_8$（$M$ =Fe，Mn）极性磁体的结构和电子性质.我们的实验数据是一致的，属于空间群P6 $_3$ mc的两个化合物的室温结构。在室温下的实验结构和电子性质在DFT+eDMFT方法中得到很好的再现，从而建立了其在顺磁相的预测能力。随着温度的降低，这两种化合物进行磁相变，我们认为，这种转变是并发的结构相变（从P6 $_3$ MC的对称性变化）的Fe化合物和同构过渡（没有从P6 $_3$ MC的对称性变化）的Mn化合物。此外，还讨论了Fe $^{2+}$离子中d-d电子跃迁的温度依赖行为。
Vibrational and Electronic Properties of Np2O5 from Experimental Spectroscopy and First Principles Calculations
Idaho National Laboratory（爱达荷国家实验室）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；Savannah River National Laboratory（萨凡纳河国家实验室）；University of Notre Dame（圣母大学）；San Diego State University（圣地亚哥州立大学）；Oak Ridge National Laboratory（橡树岭国家实验室）
