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2015
Quantization of spin-wave excitations necessitates the reconsideration of the classical fluctuation-dissipation relation (FDR) used for temperature control in spin-lattice dynamics simulations of ferromagnetic metals. In this paper, Bose-Einstein statistics is used to reinterpret the Langevin dynamics of both lattice and spins, allowing quantum sta…
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CCFE-PR(15)802015
Hubbard-like Hamiltonians are widely used to describe on-site Coulomb interactions in magnetic and stronglycorrelated solids, but there is much confusion in the literature about the form these Hamiltonians should take for shells of p and d orbitals. This paper derives the most general s , p , and d orbital Hubbard-like Hamiltonians consistent with …
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CCFE-PR(15)772015
Classical phonon scattering calculations predict the drag force acting on defects and dislocations rises linearly with temperature, in direct contradiction with molecular dynamics simulations that find the drag force to be independent of temperature for nanoscale defects. Using the Mori-Zwanzig projection technique,with no recourse to elasticity or…
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CCFE-PR(15)1202015
Low-energy magnetic states and finite-temperature properties of Cr nanoclusters in bulk bcc Fe and Fe nanoclusters in bulk Cr are investigated using density functional theory (DFT) and the Heisenberg-Landau Hamiltonian based magnetic cluster expansion (MCE). We show, by means of noncollinear magnetic DFT calculations, that magnetic frustration caus…
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CCFE-PR(15)1072015
The phase stability of fcc and bcc magnetic binary Fe-Cr, Fe-Ni, and Cr-Ni alloys, and ternary Fe-Cr-Ni alloys is investigated using a combination of density functional theory (DFT), cluster expansion (CE), and magnetic cluster expansion (MCE) approaches. Energies, magnetic moments, and volumes of more than 500 alloy structures have been evaluated …
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CCFE-PR(15)1042015
Energies of arbitrary small- and large-angle noncollinear excited magnetic configurations are computed using a highly accurate constrained density functional theory approach. Numerical convergence and accuracy are controlled by the choice of Lagrange multipliers ? I entering the constraining conditions. The penalty part E p of the constrained energ…
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CCFE-PR(15)632015
A Magnetic Cluster Expansion model for ternary face-centered cubic Fe-Ni-Cr alloys has been developed, using DFT data spanning binary and ternary alloy configurations. Using this Magnetic Cluster Expansion model Hamiltonian, we perform Monte Carlo simulations and explore magnetic structures of alloys over the entire range of compositions, consideri…
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2014
Highly mobile crystal defects such as crowdions and prismatic dislocation loops exhibit an anomalous temperature independent mobility unexplained by phonon scattering analysis. Using a projection operator, without recourse to elasticity, we derive analytic expressions for the mobility of highly mobile defects and dislocations which may be efficient…
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2014
The magnetocaloric effect in bcc iron and hcp gadolinium is simulated on pico- and nanosecond time scales using Langevin spin dynamics on a discrete lattice, with parameters determined from ab initio calculations. It is found that transient external magnetic fields can drive thermodynamic cycles even in strongly nonequilibrium spin configurations, …
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2014
A model lattice ab initio parameterized Heisenberg–Landau magnetic cluster expansion Hamiltonian spanning a broad range of alloy compositions and a large variety of chemical and magnetic configurations has been developed for face-centered cubic Fe–Ni alloys. The thermodynamic and magnetic properties of the alloys are explored using configuratio…
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