scholarly journals Theoretical confirmation of Ga-stabilized anti-ferromagnetism in plutonium metal

2014 ◽  
Vol 1683 ◽  
Author(s):  
Per Söderlind ◽  
Alex Landa
Keyword(s):  
Density Functional ◽  
Magnetic Measurements ◽  
Theory Model ◽  
Face Centered Cubic ◽  
Mechanical Instability ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
The Face ◽  
Face Centered ◽  
Plutonium Metal

ABSTRACTThe density-functional-theory model for plutonium metal is shown to be consistent with recent magnetic measurements that suggest anti-ferromagnetism in Pu-Ga alloys at low temperatures. The theoretical model predicts a stabilization of the face-centered-cubic (fcc, δ) form of plutonium in an anti-ferromagnetic configuration when alloyed with gallium. The ordered magnetic phase occurs because Ga removes the mechanical instability that exists for unalloyed δ-Pu. The cause of the Ga-induced stabilization is a combination of a lowering of the band (kinetic) and electrostatic (Coulomb) energies for the cubic relative to the tetragonal phase.

Pressure induced phase transitions in AmCm alloy

2005 ◽  
Vol 893 ◽  
Author(s):  
Sa Li ◽  
Rajeev Ahuja ◽  
Borje Johansson
Keyword(s):  
Density Functional ◽  
Alloy System ◽  
Face Centered Cubic ◽  
Generalized Gradient ◽  
Virtual Crystal Approximation ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
The Face ◽  
Face Centered ◽  
Good Agreement

AbstractWe have studied the crystal structure of the AmCm binary alloy under high pressure by means of first-principles self-consistent total-energy calculations using the generalized gradient approximation (GGA) for the density functional theory (DFT). The virtual crystal approximation (VCA) is used for the description of the alloy system. In the present study, we investigated the double hexagonal (P63/mmc) structure, the face centered cubic (Fm3m) structure, the face-centered orthorhombic (Fddd) structure and the primitive orthorhombic (Pnma) structure for the AmCm alloy. Antiferromagnetic calculations have been compared with ferromagnetic calculations for all these phases. Our results are in general good agreement with recent experiment performed by Lindbaum et al. [J. Phys.: Condens. Matter. 15, S2297 (2003)].

scholarly journals High pressure-induced distortion in face-centered cubic phase of thallium

2016 ◽  
Vol 113 (40) ◽  
pp. 11143-11147 ◽  
Author(s):  
Komsilp Kotmool ◽  
Bing Li ◽  
Sudip Chakraborty ◽  
Thiti Bovornratanaraks ◽  
Wei Luo ◽  
...  
Keyword(s):  
High Pressure ◽  
Density Functional ◽  
Cubic Phase ◽  
Face Centered Cubic ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
High Pressure Phase Transition ◽  
The Density Functional Theory ◽  
Face Centered ◽  
Mixing States

The complex and unusual high-pressure phase transition of III-A (i.e. Al, Ga, and In) metals have been investigated in the last several decades because of their interesting periodic table position between the elements having metallic and covalent bonding. Our present first principles-based electronic structure calculations and experimental investigation have revealed the unusual distortion in face-centered cubic (f.c.c.) phase of the heavy element thallium (Tl) induced by the high pressure. We have predicted body-centered tetragonal (b.c.t) phase at 83 GPa using an evolutionary algorithm coupled with ab initio calculations, and this prediction has been confirmed with a slightly distorted parameter (2 × a − c)/c lowered by 1% using an angle-dispersive X-ray diffraction technique. The density functional theory (DFT)-based calculations suggest that s–p mixing states and the valence-core overlapping of 6s and 5d states play the most important roles for the phase transitions along the pathway h.c.p→f.c.c.→b.c.t.

scholarly journals Relativistic Effects on the Equation-of-State of the Light Actinides

2005 ◽  
Vol 893 ◽  
Author(s):  
Alexander Landa ◽  
Per Söderlind
Keyword(s):  
Electronic Structure ◽  
Equation Of State ◽  
Density Functional ◽  
Relativistic Effects ◽  
Model Systems ◽  
Face Centered Cubic ◽  
Electronic Structure Methods ◽  
The Face ◽  
Face Centered ◽  
Structure Calculations

AbstractThe effect of the relativistic spin-orbit (SO)interaction on the bonding in the early actinides has been investigated by means of electronic-structure calculations. Specifically, the equation of state (EOS) for the face-centered cubic (fcc) model systems of these metals has been calculated from the first-principles density-functional (DFT) theory. Traditionally, the SO interaction in electronic-structure methods is implemented as a perturbation to the Hamiltonian that is solved for basis functions that explicitly do not depend on SO coupling. Here this approximation is shown to compare well with the fully relativistic Dirac treatment. It is further shown that SO coupling has a gradually increasing effect on the EOS as one proceeds through the actinides and the effect is diminished as density increases.

scholarly journals Influence of Si Atoms Insertion on the Formation of the Ti-Si-N Composite by DFT Simulation

2016 ◽  
Vol 12 (23) ◽  
pp. 11-23
Author(s):  
Juan Manuel Gonzalez ◽  
Johans Steeven Restrepo ◽  
Carolina Ortega Portilla ◽  
Alexander Ruden Muñoz ◽  
Federico Sequeda Osorio
Keyword(s):  
Density Functional ◽  
Amorphous Matrix ◽  
Bond Formation ◽  
Crystalline Lattice ◽  
Face Centered Cubic ◽  
Functional Theory ◽  
Dft Simulation ◽  
Face Centered ◽  
Nano Grains ◽  
Fcc Structure

Using Density Functional Theory (DFT) SiN and TiN structures were simulated, in order to study the influence of the silicon atoms insertion in the TiN lattice placed on interstitial and substitutional positions in a face centered cubic (FCC) crystalline lattice. Results showed that the SiN - FCC structure is pseudo-stable; meanwhile the tetragonal structure is stable with ceramic behavior. The TiN - FCC structure is stable with ceramic behavior similar to SiN - Tetragonal. 21% silicon atoms insertion in interstitial positions showed high induced deformation, high polarization and Si - N bond formation, indication an amorphous transition that could lead to the production of a material composed from TiN grains or nano-grains embedded in a Si - N amorphous matrix. When including 21% of silicon atoms, substituting titanium atoms, the distribution showed higher stability that could lead to the formation of different phases of the stoichiometric Ti1 -x SixNy compound.

scholarly journals Looking Beyond Adsorption Energies to Understand Interactions at Surface Using Machine Learning

2021 ◽  
Author(s):  
Sheena Agarwal ◽  
Kavita Joshi
Keyword(s):  
Machine Learning ◽  
Small Molecules ◽  
Density Functional ◽  
Mean Absolute Error ◽  
Absolute Error ◽  
Face Centered Cubic ◽  
Functional Theory ◽  
Full Picture ◽  
Adsorption Energies ◽  
Face Centered

Abstract<br>Identifying factors that influence interactions at the surface is still an active area of research. In this study, we present the importance of analyzing bondlength activation, while interpreting Density Functional Theory (DFT) results, as yet another crucial indicator for catalytic activity. We studied the<br>adsorption of small molecules, such as O 2 , N 2 , CO, and CO 2 , on seven face-centered cubic (fcc) transition metal surfaces (M = Ag, Au, Cu, Ir, Rh, Pt, and Pd) and their commonly studied facets (100, 110, and 111). Through our DFT investigations, we highlight the absence of linear correlation between adsorption energies (E ads ) and bondlength activation (BL act ). Our study indicates the importance of evaluating both to develop a better understanding of adsorption at surfaces. We also developed a Machine Learning (ML) model trained on simple periodic table properties to predict both, E ads and BL act . Our ML model gives an accuracy of Mean Absolute Error (MAE) ∼ 0.2 eV for E ads predictions and 0.02 Å for BL act predictions. The systematic study of the ML features<br>that affect E ads and BL act further reinforces the importance of looking beyond adsorption energies to get a full picture of surface interactions with DFT.<br>

Symmetry reduction of δ-plutonium: an electronic-structure effect

2005 ◽  
Vol 893 ◽  
Author(s):  
Kevin T. Moore ◽  
Per Söderlind ◽  
Adam J. Schwartz ◽  
David Laughlin
Keyword(s):  
Electronic Structure ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Monoclinic Space Group ◽  
Face Centered Cubic ◽  
Functional Theory ◽  
Space Group ◽  
Bond Strengths ◽  
Reduced Space ◽  
Face Centered

AbstractUsing first-principles density-functional theory calculations, we show that the anomalously large anisotropy of δ-plutonium is a consequence of greatly varying bond-strengths between the 12 nearest neighbors. Employing the calculated bond strengths, we expand the tenants of classical crystallography by incorporating anisotropy of chemical bonds, which yields a structure with the monoclinic space group Cm for δ-plutonium rather than face-centered cubic Fm3m. The reduced space group for δ-plutonium enlightens why the ground state of the metal is monoclinic, why distortions of the metal are viable, and has considerable implications for the behavior of the material as it ages. These results illustrate how an expansion of classical crystallography that accounts for anisotropic electronic structure can explain complicated materials in a novel way.

Theoretical Investigation of Carbon Atom Adsorption and Diffusion on the Surfaces of Cu

2014 ◽  
Vol 1082 ◽  
pp. 475-479
Author(s):  
Liang Qiao ◽  
Shu Jie Liu ◽  
Xiao Ying Hu ◽  
Li Li Wang ◽  
Dong Mei Bi
Keyword(s):  
Carbon Atom ◽  
First Principles ◽  
Density Functional ◽  
Energy Difference ◽  
Face Centered Cubic ◽  
Functional Theory ◽  
Hexagonal Close Packed ◽  
Adsorbed Carbon ◽  
Face Centered ◽  
And Diffusion

The adsorption and diffusion of carbon atom on Cu (111) and (100) surfaces have been investigated based on first-principles density-functional theory. For Cu (111) surface, the hexagonal close-packed and face-centered cubic sites are the most stable sites with little energy difference in the adsorption energy. For Cu (100) surface, the hollow site is the most stable. There is charge transfer from Cu surface to the adsorbed carbon atom. Moreover, the diffusions of carbon atom on Cu surfaces have been investigated, and the results show that the diffusion of carbon atom prefers to happen on Cu (111) surface.

scholarly journals Synthesis and Physical Properties of Iridium-Based Sulfide Ca1−xIr4S6(S2) [x = 0.23–0.33]

2022 ◽  
Vol 3 (1) ◽  
pp. 41-52
Author(s):  
Michael Vogl ◽  
Martin Valldor ◽  
Roman Boy Piening ◽  
Dmitri V. Efremov ◽  
Bernd Büchner ◽  
...  
Keyword(s):  
Density Functional ◽  
Magnetic Measurements ◽  
X Ray Diffraction ◽  
Metallic Behavior ◽  
Functional Theory ◽  
X Ray ◽  
Lattice Constants ◽  
The Density Functional Theory ◽  
Xrd Techniques

We present the synthesis and characterization of the iridium-based sulfide Ca1−xIr4S6(S2). Quality and phase analysis were conducted by means of energy-dispersive X-ray spectroscopy (EDXS) and powder X-ray diffraction (XRD) techniques. Structure analysis reveals a monoclinic symmetry with the space group C 1 2/m 1 (No. 12), with the lattice constants a = 15.030 (3) Å, b = 3.5747 (5) Å and c = 10.4572 (18) Å. Both X-ray diffraction and EDXS suggest an off-stoichiometry of calcium, leading to the empirical composition Ca1−xIr4.0S6(S2) [x = 0.23–0.33]. Transport measurements show metallic behavior of the compound in the whole range of measured temperatures. Magnetic measurements down to 1.8 K show no long range order, and Curie–Weiss analysis yields θCW = −31.4 K, suggesting that the compound undergoes a magnetic state with short range magnetic correlations. We supplement our study with calculations of the band structure in the framework of the density functional theory.

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