scholarly journals Temperature-dependent electron properties for 4f states in cerium mononitride

2021 ◽  
Author(s):  
Ru-song Li ◽  
Xiao-hua Zhou ◽  
Zheng Xie ◽  
ling-yun Kong ◽  
Deng-wu Wang ◽  
...  
Keyword(s):  
Valence State ◽  
Density Functional ◽  
Occupation Number ◽  
Mean Field Theory ◽  
Mixed Valence ◽  
Mean Field ◽  
Coulomb Repulsion ◽  
Photoemission Spectrum ◽  
Temperature Dependent ◽  
Final State

In order to elucidate the temperature-dependent valence state of Ce ion and the occupation number of Ce 4f electrons in cerium mononitride (CeN), we perform an ab initio calculation on CeN by using a many-body scheme combing density functional theory (DFT) with dynamical mean field theory (DMFT), taking into account the spin-orbit coupling (SOC) interaction and on-site Coulomb repulsion between Ce 4f electrons. Results demonstrate that Ce 4f j=5/2 and j=7/2 manifolds undergo insulating-metallic transition with the increasing of temperature. Ce 4f-conduction electrons hybridization, f-f correlation, SOC interaction and final state effects yield a complicated spectrum function in CeN. Ce 4f atomic configuration transition and hybridization might be responsible for the temperature-dependent occupancy number of Ce 4f electrons and the mixed-valence state in CeN. A fact that localization of Ce 4f electrons, i.e., 4f1 configuration or Ce3+ valence, increases with the increasing of temperature could account for the experimentally observed lattice constant versus temperature data. Finally, the so-called quasiparticle band structure is also discussed for comparison with experimental angle-resolved photoemission spectrum (ARPES).

scholarly journals Computational modeling of actinide materials and complexes

MRS Bulletin ◽  
2010 ◽  
Vol 35 (11) ◽  
pp. 883-888 ◽  
Author(s):  
Per Söderlind ◽  
G. Kotliar ◽  
K. Haule ◽  
P. M. Oppeneer ◽  
D. Guillaumont
Keyword(s):  
Density Functional ◽  
Condensed Matter ◽  
Theoretical Perspective ◽  
Mean Field Theory ◽  
Mean Field ◽  
Coulomb Repulsion ◽  
Building Blocks ◽  
Functional Theory ◽  
Electron Correlation Effects ◽  
Complex Crystal

In spite of being rare, actinide elements provide the building blocks for many fascinating condensed-matter systems, both from an experimental and theoretical perspective. Experimental observations of actinide materials are difficult because of rarity, toxicity, radioactivity, and even safety and security. Theory, on the other hand, has its own challenges. Complex crystal and electronic structures are often encountered in actinide materials, as well as pronounced electron correlation effects. Consequently, theoretical modeling of actinide materials and their 5f electronic states is very difficult. Here, we review recent theoretical efforts to describe and sometimes predict the behavior of actinide materials and complexes, such as phase stability including density functional theory (DFT), DFT in conjunction with an additional Coulomb repulsion U (DFT+U), and DFT in combination with dynamical mean-field theory (DFT+DMFT).

scholarly journals Low-temperature dielectric anomaly arising from electronic phase separation at the Mott insulator-metal transition

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
A. Pustogow ◽  
R. Rösslhuber ◽  
Y. Tan ◽  
E. Uykur ◽  
A. Böhme ◽  
...  
Keyword(s):  
Phase Separation ◽  
Mean Field Theory ◽  
Mean Field ◽  
Coulomb Repulsion ◽  
Mott Insulator ◽  
Electronic Phase Separation ◽  
First Order Phase Transition ◽  
Electronic Phase ◽  
Insulator Metal Transition ◽  
First Order Phase

AbstractCoulomb repulsion among conduction electrons in solids hinders their motion and leads to a rise in resistivity. A regime of electronic phase separation is expected at the first-order phase transition between a correlated metal and a paramagnetic Mott insulator, but remains unexplored experimentally as well as theoretically nearby T = 0. We approach this issue by assessing the complex permittivity via dielectric spectroscopy, which provides vivid mapping of the Mott transition and deep insight into its microscopic nature. Our experiments utilizing both physical pressure and chemical substitution consistently reveal a strong enhancement of the quasi-static dielectric constant ε1 when correlations are tuned through the critical value. All experimental trends are captured by dynamical mean-field theory of the single-band Hubbard model supplemented by percolation theory. Our findings suggest a similar ’dielectric catastrophe’ in many other correlated materials and explain previous observations that were assigned to multiferroicity or ferroelectricity.

Multiscale Simulations of Domains in Ferroelectrics

Domain Walls ◽  
2020 ◽  
pp. 311-339
Author(s):  
S. Liu ◽  
I. Grinberg ◽  
A. M. Rappe
Keyword(s):  
Density Functional ◽  
Large Scale ◽  
Mean Field Theory ◽  
Mean Field ◽  
Md Simulations ◽  
Relaxor Ferroelectrics ◽  
Ferroelectric Materials ◽  
Multiscale Simulations ◽  
Challenges And Opportunities ◽  
Physically Based

This chapter focuses on recent studies of ferroelectrics, where large-scale molecular dynamics (MD) simulations using first-principles-based force fields played a central role in revealing important physics inaccessible to direct density functional theory (DFT) calculations but critical for developing physically-based free energy functional for coarse-grained phase-field-type simulations. After reviewing typical atomistic potentials of ferroelectrics for MD simulations, the chapter describes a progressive theoretical framework that combines DFT, MD, and a mean-field theory. It then focuses on relaxor ferroelectrics. By examining the spatial and temporal polarization correlations in prototypical relaxor ferroelectrics with million-atom MD simulations and novel analysis techniques, this chapter shows that the widely accepted model of polar nanoregions embedded in a non-polar matrix is incorrect for Pb-based relaxors. Rather, the unusual properties of theses relaxor ferroelectrics stem from the presence of a multi-domain state with extremely small domain sizes (2–10 nanometers), giving rise to a greater flexibility for polarization rotations and the ultrahigh dielectric and piezoelectric responses. Finally, this chapter discusses the challenges and opportunities for multiscale simulations of ferroelectric materials.

Interactions between charged surfaces mediated by molecules with spatially distributed charges

2012 ◽  
Vol 85 (1) ◽  
pp. 15-26 ◽  
Author(s):  
Klemen Bohinc
Keyword(s):  
Density Functional ◽  
Mean Field Theory ◽  
Mean Field ◽  
Short Review ◽  
Molecular Shape ◽  
Attractive Force ◽  
Charge Densities ◽  
Charged Surfaces ◽  
Spatially Distributed ◽  
Rigid Rod

A short review of recent theoretical advances in studies of the interaction between highly charged systems is presented. Such a system could not be described by the mean field theory. More advanced methods have to be used in order to introduce the correlations between highly charged particles. In this work I focus on the system of highly charged surfaces, separated by a solution of molecules with spatially distributed charge. Two different representations of the molecular shape will be considered: rod-like and spherical. The system will be theoretically described by the density functional theory. For sufficiently long molecules and large surface charge densities, an attractive force between like-charged surfaces arises due to the spatially distributed charges within the molecules. The added salt has influence on the condition for the attractive force between like-charged surfaces. The theoretical results will be compared with Monte Carlo (MC) simulations. Recent measurements with multivalent rigid rod-like particles will be discussed.

Nature of Non-magnetic Strongly-Correlated State in Plutonium

2006 ◽  
Vol 986 ◽  
Author(s):  
Leniod Purovskii ◽  
Alexander Shick ◽  
Ladislav Havela ◽  
Mikhail Katsnelson ◽  
Alexander Lichtenstein
Keyword(s):  
Field Theory ◽  
Density Functional ◽  
Local Density ◽  
Mean Field Theory ◽  
Mean Field ◽  
Dynamical Mean Field Theory ◽  
Cubic Phase ◽  
Face Centered Cubic ◽  
Strongly Correlated ◽  
Starting Point

AbstractLocal density approximation for the electronic structure calculations has been highly successful for non-correlated systems. The LDA scheme quite often failed for strongly correlated materials containing transition metals and rare-earth elements with complicated charge, spin and orbital ordering. Dynamical mean field theory in combination with the first-principle scheme (LDA+DMFT) can be a starting point to go beyond static density functional approximation and include effects of charge, spin and orbital fluctuations. Ab-initio relativistic dynamical mean-field theory is applied to resolve the long-standing controversy between theory and experiment in the “simple” face-centered cubic phase of plutonium called δ-Pu. In agreement with experiment, neither static nor dynamical magnetic moments are predicted. In addition, the quasiparticle density of states reproduces not only the peak close to the Fermi level, which explains the large coefficient of electronic specific heat, but also main 5f features observed in photoelectron spectroscopy.

scholarly journals Strong enhancement of magnetic order from bulk to stretched monolayer FeSe as Hund’s metals

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Chang-Youn Moon
Keyword(s):  
Density Functional ◽  
Magnetic Order ◽  
Mean Field Theory ◽  
Mean Field ◽  
Comprehensive Understanding ◽  
Functional Theory ◽  
Iron Based Superconductors ◽  
Magnetic Orders ◽  
Spatial Isolation ◽  
Iron Based

Abstract Despite of the importance of magnetism in possible relation to other key properties in iron-based superconductors, its understanding is still far from complete especially for FeSe systems. On one hand, the origin of the absence of magnetic orders in bulk FeSe is yet to be clarified. On the other hand, it is still not clear how close monolayer FeSe on SrTiO3, with the highest transition temperature among iron-based superconductors, is to a magnetic instability. Here we investigate magnetic properties of bulk and monolayer FeSe using dynamical mean-field theory combined with density-functional theory. We find that suppressed magnetic order in bulk FeSe is associated with the reduction of interorbital charge fluctuations, an effect of Hund’s coupling, enhanced by a larger crystal-field splitting. Meanwhile, spatial isolation of Fe atoms in expanded monolayer FeSe leads into a strong magnetic order, which is completely destroyed by a small electron doping. Our work provides a comprehensive understanding of the magnetic order in iron-based superconductors and other general multi-orbital correlated systems as Hund’s metals.

MOTT TRANSITION IN THE HALF-FILLED HUBBARD MODEL ON THE HONEYCOMB LATTICE WITHIN COHERENT POTENTIAL APPROXIMATION

2013 ◽  
Vol 27 (07) ◽  
pp. 1350046 ◽  
Author(s):  
DUC ANH LE
Keyword(s):  
Hubbard Model ◽  
Quantum Monte Carlo ◽  
Mean Field Theory ◽  
Mean Field ◽  
Coulomb Repulsion ◽  
Mott Transition ◽  
Coherent Potential Approximation ◽  
Honeycomb Lattice ◽  
Potential Approximation ◽  
Good Agreement

Using the coherent potential approximation, we study zero-temperature Mott transition in the half-filled Hubbard model on the honeycomb lattice. Although a pseudogap is already present for the non-interacting case, the gap will not occur until the onsite Coulomb repulsion exceeds a critical value U ≈ 3.6t, where t is the hopping integral. When increasing U/t, the density of states at the Fermi energy first goes up gradually from zero and after reaching a maximum it goes down to zero again. Our calculated critical interaction UC/t is in very good agreement with the ones obtained by quantum Monte Carlo simulation and cluster dynamical mean-field theory.

scholarly journals BEYOND DENSITY FUNCTIONAL THEORY: THE DOMESTICATION OF NONLOCAL POTENTIALS

2004 ◽  
Vol 18 (02n03) ◽  
pp. 73-82 ◽  
Author(s):  
ROBERT K. NESBET
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Correlation Energy ◽  
Mean Field Theory ◽  
Mean Field ◽  
Energy Functional ◽  
Functional Theory ◽  
Large Molecules ◽  
Cellular Method ◽  
Nonlocal Potentials

Due to efficient scaling with electron number N, density functional theory (DFT) is widely used for studies of large molecules and solids. Restriction of an exact mean-field theory to local potential functions has recently been questioned. This review summarizes motivation for extending current DFT to include nonlocal one-electron potentials, and proposes methodology for implementation of the theory. The theoretical model, orbital functional theory (OFT), is shown to be exact in principle for the general N-electron problem. In practice it must depend on a parametrized correlation energy functional. Functionals are proposed suitable for short-range Coulomb-cusp correlation and for long-range polarization response correlation. A linearized variational cellular method (LVCM) is proposed as a common formalism for molecules and solids. Implementation of nonlocal potentials is reduced to independent calculations for each inequivalent atomic cell.

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