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Full-Text Articles in Engineering
Modified Broyden’S Method For Accelerating Convergence In Self-Consistent Calculations, Duane D. Johnson
Modified Broyden’S Method For Accelerating Convergence In Self-Consistent Calculations, Duane D. Johnson
Duane D. Johnson
A modification to Broyden’s method for obtaining stable and computationally efficient convergence in self-consistent calculations is developed and discussed. The method incorporates the advantages of two schemes proposed by Srivastava and by Vanderbilt and Louie without any increase in complexity. Its improvement over their methods is discussed. The present method is compared with two other widely used convergence methods, simple mixing and Anderson’s method, for the case of the disordered binary alloy Ni0.35Fe0.65 on the verge of a magnetic instability and is shown to be much improved in stability and rate of convergence.
Equation Of State Of Dense Helium, Richard Alan Lesar
Equation Of State Of Dense Helium, Richard Alan Lesar
Richard Alan Lesar
Comparison between pressure-volume relations in helium at high pressures indicates that theoretical calculations based on gas-phase pair potentials are not adequate to explain recent x-ray experiments. Regardless of what potential is used, the gas-phase potentials give an equation of state that is much too stiff. It is shown that if the changes in the atomic wave functions induced by the high-pressure crystal environment are taken into account, then agreement between experimental and theoretical pressure-volume curves is greatly improved.
Slip, Twinning, And Fracture At A Grain Boundary In The L12 Ordered Structure—Aς = 9 Tilt Boundary, Alexander H. King, M. H. Yoo
Slip, Twinning, And Fracture At A Grain Boundary In The L12 Ordered Structure—Aς = 9 Tilt Boundary, Alexander H. King, M. H. Yoo
Alexander H. King
The role of interaction between slip dislocations and a Σ = 9 tilt boundary in localized microplastic deformation, cleavage, or intergranular fracture in the Li2 ordered structure has been analyzed by using the anisotropic elasticity theory of dislocations and fracture. Screw superpartials cross slip easily at the boundary onto the (1$\overline 1$1) and the (001) planes at low and high temperatures, respectively. Transmission of primary slip dislocations onto the conjugate slip system occurs with a certain degree of difficulty, which is eased by localized disordering. When the transmission is impeded, cleavage fracture on the ($\overline 1$11) plane is predicted to …
New High-Pressure Phases Of Ice, Pierfranco Demontis, Richard Alan Lesar, Michael L. Klein
New High-Pressure Phases Of Ice, Pierfranco Demontis, Richard Alan Lesar, Michael L. Klein
Richard Alan Lesar
An ionic model has been used in conjunction with classical constant-pressure molecular-dynamics calculations to explore the properties of possible high-pressure phases of ice. Around 100 GPa, the model is found to convert from the symmetric hydrogen-bonded cuprite structure (ice X) to a fully ordered antifluorite structure. On heating, the new phase, ice XI, becomes a fast-ion proton conductor.
Character Of The Α-Β Phase Transition In Solid Oxygen, Richard Alan Lesar, R. D. Etters
Character Of The Α-Β Phase Transition In Solid Oxygen, Richard Alan Lesar, R. D. Etters
Richard Alan Lesar
Properties of the α and β phases of solid O2 are calculated with a deformable-cell Monte Carlo method and the character of the associated phase transition is delineated. We find that the monoclinic α phase is stable at temperatures T≲18 K and in- and out-of-plane antiferromagnetic order is predicted that is in accord with experiment. The magnetic correlations appear to be long ranged. A phase transition into β-O2 occurs at T=17.75±0.2 K. It is first order with a calculated volume change ΔV=0.06±0.10 cm3/mole, and is accompanied by a magnetic transition into a highly dynamic quasihelical state with a correlation length …
Effects Of Chemical And Magnetic Disorder In Fe0.50mn0.50, Duane D. Johnson, F. J. Pinski, G. M. Stocks
Effects Of Chemical And Magnetic Disorder In Fe0.50mn0.50, Duane D. Johnson, F. J. Pinski, G. M. Stocks
Duane D. Johnson
We present the results of first‐principles calculations of the total energy and spin‐polarized electronic structure of disordered fcc Fe0.50Mn0.50. These self‐consistent calculations were performed using the Korringa–Kohn–Rostoker method and the coherent‐potential approximation (KKR‐CPA), using the local‐spin‐density approximation to treat exchange and correlation. We use a lattice constant of a=6.80 a.u.; information about stability can be inferred from calculated pressure and energy. The moments on the Fe and Mn sites are large but antiparallel to each other, resulting in a small net magnetization. A comparison of the electronic structure is made for fcc Fe, Mn, and FeMn in both the ferromagnetic …
Theoretical Study Of The Hyperfine Fields Of Ni And Fe In Fcc Ni,Fe, Alloys, H. Ebert, H. Winter, B. L. Gyorffy, Duane D. Johnson, F. J. Pinski
Theoretical Study Of The Hyperfine Fields Of Ni And Fe In Fcc Ni,Fe, Alloys, H. Ebert, H. Winter, B. L. Gyorffy, Duane D. Johnson, F. J. Pinski
Duane D. Johnson
Using charge self-consistent cluster Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) band-structure calculations, the authors have studied the hyperfine fields on both Ni and Fe sites in the NixFe1-x alloys. To elucidate the influence of relativistic effects the hyperfine matrix elements have been calculated nonrelativistically as well as completely relativistically The dependence of the hyperfine fields on the environment of a given site has been studied by performing calculations for various atomic configurations around that site. The results of the work are compared with other theoretical data and with experiment.
Thermodynamic Properties And Equation Of State Of Dense Fluid Nitrogen, J. Belak, R. D. Etters, Richard Alan Lesar
Thermodynamic Properties And Equation Of State Of Dense Fluid Nitrogen, J. Belak, R. D. Etters, Richard Alan Lesar
Richard Alan Lesar
Results of constant‐pressure Monte Carlo calculations on dense fluid nitrogen over a pressure range of 2 to 300 kbar and a temperature range of 300–3000 K are presented. From analytic fits to the calculated volumes, enthalpies and vibrational frequency shifts, a comprehensive set of thermodynamic quantities is derived, including: thermal expansivity, compressibility, specific heat, Grüneisen parameter, and speed of sound. Comparison of the theoretical results to experiment at room temperature shows very good agreement (within 0.3% in volume and 1% in speed of sound, for instance). Good agreement is also obtained with earlier simulation data. In agreement with experimental studies …