Magnetic properties of Li$_x$CoO$_2$ for $x = 0.94, 0.75, 0.66$ and $0.51$ were investigated in frames of method combining Generalized Gradient Approximation with Dynamical Mean--Field Theory (GGA+DMFT). We found that a delicate interplay between Hund's exchange energy and $t_{2g}-e_g$ crystal field splitting is responsible for the high spin to low spin state transition for Co$^{4+}$ ions. The GGA+DMFT calculations show that at small doping level the Co$^{4+}$ ions adopt high spin state, while delithiation results in increase of the crystal field splitting and low spin state becomes preferable. The Co$^{3+}$ ions were found to stays in the low spin configuration for any $x$.
We present the band structure of CeIr$_3$ superconductor calculated within the dynamical mean field theory (DMFT). Standard GGA and GGA+U methods fail to reproduce the experimental electronic specific heat coefficient $γ_{\rm expt.}$ due to the underestimated density of states at the Fermi level $N(E_F)$ followed by an overestimated strength of electron-phonon coupling (EPC) calculated as a renormalization of $γ_{\rm expt.}$. The DMFT study shows a strong hybridization of $4f$ states of Ce with $5d$-states of Ir, which leads to the larger $N(E_F)$ giving the correct $γ_{\rm expt.}$ with a mode…
We report complex band structure (CBS) calculations for the four late transition metal monoxides, MnO, FeO, CoO and NiO, in their paramagnetic phase. The CBS is obtained from density functional theory plus dynamical mean field theory (DMFT) calculations to take into account correlation effects. The so-called $β$ parameters, governing the exponential decay of the transmission probability in the non-resonant tunneling regime of these oxides, are extracted from the CBS. Different model constructions are examined in the DMFT part of the calculation. The calculated $β$ parameters provide theoretica…
Dynamical Mean-Field Theory (DMFT) has opened new perspectives for the investigation of strongly correlated electron systems and greatly improved our understanding of correlation effects in models and materials. In contrast to Hartree-Fock-type approximations the mean field of DMFT is dynamical, whereby local quantum fluctuations are fully taken into account. DMFT becomes exact in the limit of high spatial dimensions or coordination number. Using DMFT the dynamics of correlated electron systems can be investigated non-perturbatively at all interaction strengths, electron densities and temperat…
A comparative study of the magnetocaloric effect (MCE) in metals within the single-band Hubbard model on the face-centered cubic (fcc) lattice using both mean-field (Stoner) approximation (MFA) and dynamical mean-field theory (DMFT) is done. The MCE is investigated in the case of second order magnetic phase transition from ferromagnet to paramagnet. To ensure presence of itinerant ferromagnetism in the Hubbard model the special case of spectrum parameters generating giant van Hove singularity at the bottom of the band is considered, while the Fermi level $E_{\rm f}$ is in the vinicity of the b…
Many-body renormalisation of forces in f-electron materials
给出了动态平均场论在CASTEP \emph{ab-initio}程序中的实现.我们详细解释了DFT+DMFT的理论框架，我们证明了我们的实施与$f$壳层电子的三个强相关系统：$γ$ -铈，铈倍半氧化物Ce $_{2}$ O $_{3}$和碲化钐SmTe通过使用哈伯德我解算器。我们发现非常好的协议与以前的基准DFT+DMFT计算的铈化合物，而SmTe，这是从来没有在DFT+DMFT研究之前，据我们所知，我们表现出改进的协议与实验结构参数相比，LDA。我们的实现同样适用于规范守恒和超软赝势，我们将其应用到计算的总能量，体积模量，平衡体积和内力在两个铈化合物。在Ce $_{2}$ O $_{3}$中，我们报告了作用于不受晶胞对称性约束的坐标上的内力的急剧减少。这种减少是由多体效应引起的，只能在DMFT水平上捕获。此外，我们推导出另一种形式来处理高频尾巴的格林函数在松原频率求和。我们的治疗允许减少的偏见时，计算的相关能量和占领矩阵，以高精度。
We study theoretically low-temperature phases of a recently synthesized compound Sr$_2$CoO$_3$F under pressure. The analysis combining LDA+DMFT and a strong-coupling effective model points to the existence of not only normal paramagnetic and antiferromagnetic regimes, but also a spin-state ordered phase in a certain range of applied pressure and low temperature. This order is characterized by a checkerboard arrangement of different spin states of cobalt atoms in the lattice.
Magnetic instabilities in three- and higher-dimensional Hubbard models with different lattice geometries: Impact of nonlocal spatial correlations
Institute of Theoretical Physics, University of Hamburg（汉堡大学理论物理研究所）；Institute of Solid State Physics, TU Wien（维也纳工业大学固体物理研究所）；Institute for Theoretical Solid State Physics, Leibniz Institute for Solid State and Materials Research Dresden（德累斯顿莱布尼茨固体与材料研究所理论固体物理研究所）；Institut für Theoretische Physik und Astrophysik and Würzburg-Dresden Cluster of Excellence ctd.qmat, Universität Würzburg（维尔茨堡大学理论物理与天体物理学系及维尔茨堡-德累塞尔卓越集群ctd.qmat）；Theory and Simulation of Condensed Matter, Department of Physics, King’s College London（伦敦国王学院物理系凝聚态理论与模拟组）
We present a short review of our studies of disorder influence upon Ginzburg - Landau expansion coefficients in Anderson - Hubbard model with attraction in the framework of the generalized DMFT+$Σ$ approximation. A wide range of attractive potentials $U$ is considered - from weak coupling limit, where superconductivity is described by BCS model, to the limit of very strong coupling, where superconducting transition is related to Bose - Einstein condensation (BEC) of compact Cooper pairs, which are formed at temperatures significantly higher than the temperature of superconducting transition, a…
