Pui-Wai Ma S. L. Dudarev
CALANIE (CALculation of ANIsotropic Elastic energy) program evaluates an elastic interaction correction to the total energy of a localized object, for example a defect in a solid material simulated using an {it ab initio} or molecular statics approach, resulting from the use of periodic boundary conditions. The correction, computed using a fully el…
Preprint PublishedJ. Chapman Pui-Wai Ma S. L. Dudarev
Magnetic plasma confinement is a key element of fusion tokamak power plant design, yet changes in magnetic properties of alloys and steels occurring under neutron irradiation are often overlooked. We perform a quantitative study exploring how irradiation-induced precipitation affects magnetic properties of Fe-Cr alloys. Magnetic properties are simu…
Preprint PublishedS. L. Dudarev Pui-Wai Ma
Density functional theory (DFT) calculations show that self-interstitial atom defects in nonmagnetic body-centred cubic (bcc) metals adopt strongly anisotropic configurations, elongated in the h111i direction1–4. Elastic distortions, associated with such anisotropic defect configurations, appear similar to the distortions around small prismatic d…
Preprint PurchasePui-Wai Ma S.L. Dudarev C.H. Woo
Spin–lattice dynamics generalizes molecular dynamics to magnetic materials, where dynamic variables describing an evolving atomic system include not only coordinates and velocities of atoms but also directions and magnitudes of atomic magnetic moments (spins). Spin–lattice dynamics simulates the collective time evolution of spins and atoms, tak…
PublishedC. H. Woo Haohua Wen A. A. Semenov S. L. Dudarev Pui-Wai Ma
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…
PublishedM. E. A. Coury S. L. Dudarev W. M. C. Foulkes A. P. Horsfield Pui-Wai Ma J. S. Spencer
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 …
Preprint PublishedM. Pui-Wai S. L. Dudarev
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…
Preprint PublishedPui-Wai Ma S. L. Dudarev
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, …
PublishedD. Nguyen-Manh Pui-Wai Ma M.Yu. Lavrentiev S.L. Dudarev
The development of quantitative models for radiation damage effects in iron, iron alloys and steels, particularly for the high temperature properties of the alloys, requires understanding of magnetic interactions, which control the phase stability of ferritic-martensitic, ferritic, and austenitic steels. In this work, disordered magnetic configurat…
PublishedPui-Wai Ma S. L. Dudarev
We develop a generalized Langevin spin dynamics (GLSD) algorithm where both the longitudinal and transverse (rotational) degrees of freedom of atomic magnetic moments are treated as dynamic variables. This removes the fundamental limitation associated with the use of stochastic Landau-Lifshitz (sLL) equations, in which the magnitude of magnetic mom…
Published