First-principles phonon calculations along with density functional theory (DFT) play an important role to study the dynamical and thermal properties of materials. Here, we investigate the effect of exchange correlation (XC) functionals on the vibrational and thermodynamic properties of CoSi. The role of 3s(2p) orbitals of Co(Si) as core/valence states on the phonon properties of this compound is also studied. Phonon calculations are carried out by finite displacement method with supercell approach using equilibrium crystal structures obtained from DFT calculations. The calculated results are compared with the existing experiment. Three XC functionals, viz., LDA, PBEsol and SCAN are used for calculating the phonon dispersion, phonon density of states (DOS)/partial DOS and thermal properties of this compound. SCAN is found to give the highest phonon frequency of $\sim$56 meV which is in good agreement with the experimental value, while LDA (PBEsol) gives $\sim$54 ($\sim$55) meV. The zero-point energy is calculated as $\sim$ 10 kJ/mol for all the functionals. The Debye temperatures ($Θ_{D}$) are computed as $\sim$626 K, $\sim$638 K and $\sim$650 K for LDA, PBEsol and SCAN, respectively. The $Θ_{D}$ obtained from LDA gives the good agreement with the reported value. The phonon dispersion and phonon DOS are found to be dependent whether 3s(2p) orbitals of Co(Si) are considered as core or valence states. But, this orbital dependency is seemed to be insignificant on the thermal properties of this compound.
A theoretically supported experimental study of the (1-x)LaFeO3.xLaMnO3 (LFO-LMO) solid solution is being reported for the first time which reveals a phase transformation from the Pbnm and R3-c phase at a chemical composition of x=0.625. Correlation of octahedral distortion and phase transition was extensively investigated using x-ray photoelectron spectroscopy (XPS), Raman and x-ray diffraction (XRD) measurements and density functional theory (DFT) calculation. A detailed study of the structural lattice parameters, bond lengths, bond angles have been done, supported by valence state and elect…
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）
Present work provides extensive DFT study of TlReO4 using pseudopotential approach for understanding the structural and vibrational properties and full-potential linearized augmented plane wave method for electronic band structure and associated optical properties. Calculated bulk modulus value 29.77 GPa using LDA functional is found to be close to experimental value 26 GPa. The order of elastic constant along the principal axis clearly indicates the crucial role of Re and O3 atoms in the structural and mechanical properties of this material. Analysis of Born effective charge (BEC) along with …
Leibniz-Institut für Kristallzüchtung (IKZ)（莱布尼茨晶体生长研究所）；Center for Computational Materials Science, United States Naval Research Laboratory（美国海军研究实验室计算材料科学中心）；Institute of Experimental Physics, TU Bergakademie Freiberg（弗莱贝格矿业技术大学实验物理研究所）；Ferdinand-Braun-Institut (FBH)（费迪南德·布劳恩研究所）；Institute of Solid State Physics, Technische Universität Berlin（柏林工业大学固体物理研究所）；Technische Physik, University of Würzburg（维尔茨堡大学技术物理系）
This work examines the carbon defects associated with recently reported and novel peaks of infrared (IR) absorption and Raman scattering appearing in GaN crystals at carbon ($^{12}C$) doping in the range of concentrations from $3.2*10^{17}$ to $3.5*10^{19} cm^{-3}$. 14 unique vibrational modes of defects are observed in GaN samples grown by hydride vapor phase epitaxy (HVPE) and then compared with defect properties predicted from first-principles calculations. The vibrational frequency shift in two $^{13}C$ enriched samples related to the effect of the isotope mass indicates six distinct confi…
Brillouin zone unfolding method for effective phonon spectra
热性质在现代电子器件和纳米结构中具有重要意义。当设备由纯材料制成时，计算这些属性是简单的，但当使用合金时就会出现问题。具体来说，只有近似能带结构可以计算随机合金和最常见的虚拟晶体近似（VCA）使用。展开方法[T. B. Boykin，N.哈尔切湾Klimeck和M. Korkusinski，J. Phys.：康登斯马太福音19，036203（2007）.]已被证明是非常有用的紧束缚计算的合金电子结构，没有在VCA的问题，和紧束缚和价力场方法之间的声子问题的数学类比表明，他们在这里也被采用。然而，这两个问题的物理性质存在一些差异，需要对电子结构方法进行修改。因此，我们推导出一个声子合金能带结构（振动模式）的方法，我们的紧束缚电子结构方法的基础上，修改带测定方法，以适应不同的物理情况。利用这种方法，我们研究了In $_x$ Ga $_{1-x}$ As合金，发现与现有的实验结果非常吻合。
We calculate the lattice thermal conductivities of the pyrite-type ZnSe2 at pressures of 0 and 10 GPa using the linearized phonon Boltzmann transport equation. We obtain a very low value [0.69 W/(mK) at room temperature at 0 GPa], comparable to the best thermoelectric materials. The vibrational spectrum is characterized by the isolated high-frequency optical phonon modes due to the stretching of Se-Se dimers and low-frequency optical phonon modes due to the rotation of Zn atoms around these dimers. The low-frequency optical phonon modes are characterized by a strong anharmonicity and will subs…
The thermoelectric properties of the three pyrite-type IIB-VIA2 dichalcogenides (ZnS2, CdS2 and CdSe2) are systematically investigated and compared with those of the prototype ZnSe2 in order to optimize their thermoelectric properties. Using the phonon Boltzmann transport equation, we find that they all have ultralow lattice thermal conductivities. By analyzing their vibrational properties, these are attributed to soft phonon modes derived from the loosely bound rattling-like metal atoms and to strong anharmonicities caused by the vibrations of all atoms perpendicular to the strongly bound non…
