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Articles 1  30 of 57
FullText Articles in Physics
Structural, Magnetic, And Defect Properties Of CoPtType MagneticStorage Alloys: DensityFunctional Theory Study Of Thermal Processing Effects, Aftab Alam, Brent Kraczek, Duane D. Johnson
Structural, Magnetic, And Defect Properties Of CoPtType MagneticStorage Alloys: DensityFunctional Theory Study Of Thermal Processing Effects, Aftab Alam, Brent Kraczek, Duane D. Johnson
Duane D. Johnson
Using an optimizedbasis KorringaKohnRostokercoherentpotential approximation method, we calculate formation enthalpies ΔEf, structural, and magnetic properties of paramagnetic (PM) and ferromagnetic, disordered A1 and ordered L10 CoPt, FePd, and FePt systems that are of interest for highdensity magneticrecording media. To address processing effects, we focus on the point defects that dictate thermal properties and planar defects (e.g., c domain and antiphase boundaries) which can serve as pinning centers for magnetic domains and affect storage properties. We determine bulk Curie (Tc) and orderdisorder (Tod) transition temperatures within 4% of observed values, and estimates for nanoparticles. Planardefect energies γhklx show that the ...
Preparation And Characterization Of Pt/ΓAl2o3 Model Catalyst On Nial Alloy, Zhongfan Zhang, Long Li, LinLin Wang, Sergio I. Sanchez, Ross V. Grieshaber, Qi Wang, Duane D. Johnson, Anatoly I. Frenkel, Ralph G. Nuzzo, Judith C. Yang
Preparation And Characterization Of Pt/ΓAl2o3 Model Catalyst On Nial Alloy, Zhongfan Zhang, Long Li, LinLin Wang, Sergio I. Sanchez, Ross V. Grieshaber, Qi Wang, Duane D. Johnson, Anatoly I. Frenkel, Ralph G. Nuzzo, Judith C. Yang
Duane D. Johnson
Numerous studies of heterogeneous catalysis systems clearly demonstrate that the metal nanoparticle (NPs)/support interaction is significant in determining the catalytic chemistry. Theoretical simulations have been performed to understand the metal/support interactions [1,2]. For example, theorists discovered that electronic and oxygen defects of γAl2O3 anchor the active particles [1]. Platinum NPs dispersed on γalumina is one of the most widely used heterogeneous catalysts and Pt performs extremely well as a catalyst for the oxygenreduction reaction used in fuel cell industries. Hence, we chose Pt/γAl2O3 as a model heterogeneous catalyst system to investigate the metal NPs/support interface ...
Interphase Energies Of Hcp Precipitates In Fcc Metals: A DensityFunctional Theory Study In AlAg, Daniel Finkenstadt, Duane D. Johnson
Interphase Energies Of Hcp Precipitates In Fcc Metals: A DensityFunctional Theory Study In AlAg, Daniel Finkenstadt, Duane D. Johnson
Duane D. Johnson
Densityfunctional theory (DFT) calculations of interphase boundary energies relevant to hexagonalclosepacked (hcp) γprecipitate formation were performed within approximate unit cells that mirror the experimental conditions in facecenteredcubic (fcc) AlAg solid solutions. In Alrich, fcc AlAg, γ precipitates are observed to form rapidly with large (300+) aspect ratios even though the Al stackingfault energy is high (approximately 130 mJ/m2), which should suppress hcp ribbon formation according to standard arguments. Our DFT results show why highaspect ratio plates occur and why previous estimates based on Wulff construction were orders of magnitude less than observed values. Using DFT, we obtain a Gibbs ...
Analysis Of Nonequilibrium Hcp Precipitate Growth In Fcc Matrices: Application To Al–Ag, Daniel Finkenstadt, Duane D. Johnson
Analysis Of Nonequilibrium Hcp Precipitate Growth In Fcc Matrices: Application To Al–Ag, Daniel Finkenstadt, Duane D. Johnson
Duane D. Johnson
Hexagonalclosepacked (hcp) γprecipitates with large aspect ratios form rapidly in some facecentered cubic (fcc) solidsolutions. No model explains the observed timedependent increase in aspect ratio, nor irregular intermediate growth shapes. We propose a nonequilibrium process involving trapezoidal offshoots (controlled only by energetics) that governs the growth behavior (kinetics) and yields nonequilibrium structures in agreement with observation. Then, combining nucleation theory and diffusionlimited growth both of secondary nuclei and ledges, we derive a general growth equation for γprecipitates due to solutesegregation to precipitate–matrix interfaces that includes our modification of the Jones–Trivedi model for thickening to account for the slow ...
Optimal SiteCentered Electronic Structure Basis Set From A DisplacedCenter Expansion: Improved Results Via A Priori Estimates Of Saddle Points In The Density, Aftab Alam, Duane D. Johnson
Optimal SiteCentered Electronic Structure Basis Set From A DisplacedCenter Expansion: Improved Results Via A Priori Estimates Of Saddle Points In The Density, Aftab Alam, Duane D. Johnson
Duane D. Johnson
Sitecentered, electronicstructure methods use an expansion inside nonoverlapping “muffintin” (MT) spheres plus an interstitial basis set. As the boundary separating the more spherical from nonspherical density between atoms, the “saddlepoint” radii (SPR) in the density provide an optimal spherical region for expanding in spherical harmonics, as used in augmented plane wave, muffintin orbital, and multiplescattering [Korringa, Kohn, and Rostoker (KKR)] methods. These MTSPR guarantee unique, convex Voronoi polyhedra at each site, in distinction to Bader topological cells. We present a numerically fast, twocenter expansion to find SPR a priori from overlapping atomic charge densities, valid also for disordered alloys. We ...
Surface Geometry Of C60 On Ag(111), H. I. Li, K. Pussi, K. J. Hanna, LinLin Wang, Duane D. Johnson, H.P. Cheng, H. Shin, S. Curtarolo, W. Moritz, J. A. Smerdon, R. Mcgrath, R. D. Diehl
Surface Geometry Of C60 On Ag(111), H. I. Li, K. Pussi, K. J. Hanna, LinLin Wang, Duane D. Johnson, H.P. Cheng, H. Shin, S. Curtarolo, W. Moritz, J. A. Smerdon, R. Mcgrath, R. D. Diehl
Duane D. Johnson
The geometry of adsorbed C60 influences its collective properties. We report the first dynamical lowenergy electron diffraction study to determine the geometry of a C60 monolayer, Ag(111)−(23√×23√)30°−C60, and related density functional theory calculations. The stable monolayer has C60 molecules in vacancies that result from the displacement of surface atoms. C60 bonds with hexagons down, with their mirror planes parallel to that of the substrate. The results indicate that vacancy structures are the rule rather than the exception for C60 monolayers on closepacked metal surfaces.
Quantitative Prediction Of Twinning Stress In Fcc Alloys: Application To CuAl, Sandeep A. Kibey, LinLin Wang, J. B. Liu, H. T. Johnson, H. Sehitoglu, Duane D. Johnson
Quantitative Prediction Of Twinning Stress In Fcc Alloys: Application To CuAl, Sandeep A. Kibey, LinLin Wang, J. B. Liu, H. T. Johnson, H. Sehitoglu, Duane D. Johnson
Duane D. Johnson
Twinning is one of most prevalent deformation mechanisms in materials. Having established a quantitative theory to predict onset twinning stress τcrit in fcc elemental metals from their generalized planarfaultenergy (GPFE) surface, we exemplify its use in alloys where the Suzuki effect (i.e., solute energetically favors residing at and near planar faults) is operative; specifically, we apply it in CuxAl (x is 0, 5, and 8.3 at. %) in comparison with experimental data. We compute the GPFE via densityfunctional theory, and we predict the solute dependence of the GPFE and τcrit, in agreement with measured values. We show that τcrit ...
BccToHcp Transformation Pathways For Iron Versus Hydrostatic Pressure: Coupled Shuffle And Shear Modes, J. B. Liu, Duane D. Johnson
BccToHcp Transformation Pathways For Iron Versus Hydrostatic Pressure: Coupled Shuffle And Shear Modes, J. B. Liu, Duane D. Johnson
Duane D. Johnson
Using densityfunctional theory, we calculate the potentialenergy surface (PES), minimumenergy pathway (MEP), and transition state (TS) versus hydrostatic pressure σhyd for the reconstructive transformation in Fe from bodycentered cubic (bcc) to hexagonal closedpacked (hcp). At fixed σhyd, the PES is described by coupled shear (ϵ) and shuffle (η) modes and is determined from structurally minimized hcpbcc energy differences at a set of (η,ϵ). We fit the PES using symmetryadapted polynomials, permitting the MEP to be found analytically. The MEP is continuous and fully explains the transformation and its associated magnetization and volume discontinuity at TS. We show that σhyd ...
LowEnergy Antiphase Boundaries, Degenerate Superstructures, And Phase Stability In Frustrated Fcc Ising Model And AgAu Alloys, Nikolai A. Zarkevich, Teck L. Tan, LinLin Wang, Duane D. Johnson
LowEnergy Antiphase Boundaries, Degenerate Superstructures, And Phase Stability In Frustrated Fcc Ising Model And AgAu Alloys, Nikolai A. Zarkevich, Teck L. Tan, LinLin Wang, Duane D. Johnson
Duane D. Johnson
An Ising model exhibits zeroenergy antiphase boundaries (APBs) and frustration on closepacked facecentered cubic (fcc) and triangular lattices. The frustration results in degenerate structures and chains of longperiod superstructures forming a quasicontinuous groundstate “hull” in the formation energy versus composition (c) diagram. In alloys, a nonzero but small APB energy yields a cdependent reduction in this degeneracy that affects the phase diagram topology and range of the twophase coexistence. Using density functional theory combined with cluster expansions (CEs), we study AgAu alloys as a prototype and find the effective cluster interactions (dominated by nearestneighbor pairs), predict energetics of millions of ...
Predicting Enthalpies Of Molecular Substances: Application To Libh4, Nikolai A. Zarkevich, Duane D. Johnson
Predicting Enthalpies Of Molecular Substances: Application To Libh4, Nikolai A. Zarkevich, Duane D. Johnson
Duane D. Johnson
For molecular substances exhibiting harmonic and nonharmonic vibrations, we present a firstprinciples approach to predict enthalpy differences between phases at finite temperatures, including solidsolid and melting. We apply it to the complex hydride LiBH4. Using ab initio molecular dynamics, we predict a structure for the highT solid phase of lithium borohydride, and we propose an approximation to account for nonharmonic vibrations. We then predict the enthalpy changes for solidsolid transition, melting, and an Hstorage reaction, all in agreement with experiment.
Density Functional Study Of Structural Trends For LateTransitionMetal 13Atom Clusters, LinLin Wang, Duane D. Johnson
Density Functional Study Of Structural Trends For LateTransitionMetal 13Atom Clusters, LinLin Wang, Duane D. Johnson
Duane D. Johnson
Because reactivity increases as particle size decreases and competition between numerous structures are possible, which affects catalytic and magnetic properties, we study the structural trends of latetransitionmetal 13atom clusters using density functional theory within the generalized gradient approximation to exchangecorrelation functional. We consider open structural motifs, such as bilayer and cubic (recently found to have lower energy), and find new bilayer candidates that are even lower in energy. To study the influence of dorbital filling on structural trends, we focus on Pt, Pd, and Rh clusters and find several new, lowenergy structures for Pt13 and Pd13 from searches using a ...
Comment On “Structural Stability Of Complex Hydrides: Libh4 Revisited”, Duane D. Johnson, Nikolai A. Zarkevich
Comment On “Structural Stability Of Complex Hydrides: Libh4 Revisited”, Duane D. Johnson, Nikolai A. Zarkevich
Duane D. Johnson
A Comment on the Letter by Zbigniew Łodziana and Tejs Vegge, Phys. Rev. Lett. 93, 145501 (2004).
Generalized Planar Fault Energies And Twinning In Cu–Al Alloys, S. Kibey, J. B. Liu, Duane D. Johnson, H. Sehitoglu
Generalized Planar Fault Energies And Twinning In Cu–Al Alloys, S. Kibey, J. B. Liu, Duane D. Johnson, H. Sehitoglu
Duane D. Johnson
We report ab initio density functional theory calculations of generalized planar fault energies of fcc Cu–xAl (x=0, 5.0, and 8.3at.%) alloys. We investigate the effects of substitutional solute Al on the unstable intrinsic γus and twin γutstacking faultenergies (SFEs). Our results reveal an increased tendency of Cu–Al to deform preferentially by twinning with increasing Al content, consistent with experiment. We attribute this mechanical behavior to appreciable lowering of the twinning barrier γut, along with the stable intrinsic and twin SFEs.
Solute/DefectMediated Pathway For Rapid Nanoprecipitation In Solid Solutions: Γ Surface Analysis In Fcc AlAg, Daniel Finkenstadt, Duane D. Johnson
Solute/DefectMediated Pathway For Rapid Nanoprecipitation In Solid Solutions: Γ Surface Analysis In Fcc AlAg, Daniel Finkenstadt, Duane D. Johnson
Duane D. Johnson
In facecenteredcubic (fcc) Al, stacking fault energy (SFE) is high at ca. 150mJ/m2, inhibiting stacking fault (SF) formation and dislocation motion. Yet Agrich hcp precipitates form rapidly in Alrich fcc AlAg, even as the energy difference ΔEhcp−fcc between hcp and fcc homogeneous solid solution increases with Ag content. Using electronic density functional theory methods, we calculate the SFE γSF versus distance of Ag (111) planes from intrinsic (isf), extrinsic (esf) and twin (tsf) SFs. We find that an inhomogeneous distribution of Ag solute segregated in layers adjacent to SFs leads to favorable SFE, a manifestation of the wellknown ...
Recycling Krylov Subspaces For Sequences Of Linear Systems, Michael L. Parks, Eric De Sturler, Greg Mackey, Duane D. Johnson, Spandan Maiti
Recycling Krylov Subspaces For Sequences Of Linear Systems, Michael L. Parks, Eric De Sturler, Greg Mackey, Duane D. Johnson, Spandan Maiti
Duane D. Johnson
Many problems in science and engineering require the solution of a long sequence of slowly changing linear systems. We propose and analyze two methods that significantly reduce the total number of matrix‐vector products required to solve all systems. We consider the general case where both the matrix and right‐hand side change, and we make no assumptions regarding the change in the right‐hand sides. Furthermore, we consider general nonsingular matrices, and we do not assume that all matrices are pairwise close or that the sequence of matrices converges to a particular matrix. Our methods work well under these ...
Systematic, Multisite ShortRangeOrder Corrections To The Electronic Structure Of Disordered Alloys From First Principles: The Kkr Nonlocal Cpa From The Dynamical Cluster Approximation, D. A. Biava, Subhradip Ghosh, Duane D. Johnson, W. A. Shelton, Andrei V. Smirnov
Systematic, Multisite ShortRangeOrder Corrections To The Electronic Structure Of Disordered Alloys From First Principles: The Kkr Nonlocal Cpa From The Dynamical Cluster Approximation, D. A. Biava, Subhradip Ghosh, Duane D. Johnson, W. A. Shelton, Andrei V. Smirnov
Duane D. Johnson
Although the KorringaKohnRostoker coherentpotential approximation (KKRCPA) is used widely to configurationally average and get electronic structures and energies of disordered alloys, a singlesite CPA misses local environment effects, including shortrange order (SRO). A proposed nonlocal CPA (NLCPA) recovers translational invariance of the effective medium via kspace coarse graining from the dynamical cluster approximation (DCA), where corrections are systematic as cluster size increases. We implement a firstprinciples KKRNLCPA/DCA and show the effects of environment, including SRO, on the electronic structures of fcc CuAu and bcc NiAl.
Genetic Programming For Multitimescale Modeling, Kumara Sastry, Duane D. Johnson, David E. Goldberg, Pascal Bellon
Genetic Programming For Multitimescale Modeling, Kumara Sastry, Duane D. Johnson, David E. Goldberg, Pascal Bellon
Duane D. Johnson
A bottleneck for multitimescale thermally activated dynamics is the computation of the potential energy surface. We explore the use of genetic programming (GP) to symbolically regress a mapping of the saddlepoint barriers from only a few calculated points via molecular dynamics, thereby avoiding explicit calculation of all barriers. The GPregressed barrier function enables use of kinetic Monte Carlo to simulate realtime kinetics (seconds to hours) based upon realistic atomic interactions. To illustrate the concept, we apply a GP regression to vacancyassisted migration on a surface of a concentrated binary alloy (from both quantum and empirical potentials) and predict the diffusion ...
Crossover Energetics For Halogenated Si(100): Vacancy Line Defects, Dimer Vacancy Lines, And Atom Vacancy Lines, G. J. Xu, Nikolai A. Zarkevich, Abhishek Agrawal, A. W. Signore, B. R. Trenhaile, Duane D. Johnson, J. H. Weaver
Crossover Energetics For Halogenated Si(100): Vacancy Line Defects, Dimer Vacancy Lines, And Atom Vacancy Lines, G. J. Xu, Nikolai A. Zarkevich, Abhishek Agrawal, A. W. Signore, B. R. Trenhaile, Duane D. Johnson, J. H. Weaver
Duane D. Johnson
We investigated surface patterning of ISi(100)(2×1) both experimentally and theoretically. Using scanning tunneling microscopy, we first examined I destabilization of Si(100)(2×1) at near saturation. Dimer vacancies formed on the terraces at 600 K, and they grew into lines that were perpendicular to the dimer rows, termed vacancy line defects. These patterns were distinctive from those induced by Cl and Br under similar conditions since the latter formed atom and dimer vacancy lines that were parallel to the dimer rows. Using firstprinciples density functional theory, we determined the steric repulsive interactions associated with iodine and ...
Importance Of Thermal Disorder On The Properties Of Alloys: Origin Of Paramagnetism And Structural Anomalies In BccBased Fe1−Xalx, Andrei V. Smirnov, W. A. Shelton, Duane D. Johnson
Importance Of Thermal Disorder On The Properties Of Alloys: Origin Of Paramagnetism And Structural Anomalies In BccBased Fe1−Xalx, Andrei V. Smirnov, W. A. Shelton, Duane D. Johnson
Duane D. Johnson
Fe1−xAlx exhibits interesting magnetic and anomalous structural properties as a function of composition and sample processing conditions arising from thermal or offstoichiometric chemical disorder, and, although well studied, these properties are not understood. In stoichiometric B2 FeAl, including the effects of partial longrange order, i.e., thermal antisites, we find the experimentally observed paramagnetic response with nonzero local moments, in contrast to past investigations that find either a ferromagnetic or nonmagnetic state, both inconsistent with experiment. Moreover, from this magnetochemical coupling, we are able to determine the origins of the observed lattice constant anomalies found in Fe1−xAlx for ...
Prediction Of Dopant Ionization Energies In Silicon: The Importance Of Strain, A. Rockett, Duane D. Johnson, S. V. Khare, B. R. Tuttle
Prediction Of Dopant Ionization Energies In Silicon: The Importance Of Strain, A. Rockett, Duane D. Johnson, S. V. Khare, B. R. Tuttle
Duane D. Johnson
Based on a hydrogenic state and strain changes upon defect charging, we propose a simple, parameterfree model that agrees well with the observed group III and V monovalentimpurity ionization energies in Si, revealing the importance of such strain effects. Changes in lattice strain upon defect charging are obtained via superposition and elasticity theory using atomic relaxations from density functional theory.
Competition Between Ferromagnetism And Antiferromagnetism In Fept, G. Brown, B. Kraczek, A. Janotti, T. C. Schulthess, G. M. Stocks, Duane D. Johnson
Competition Between Ferromagnetism And Antiferromagnetism In Fept, G. Brown, B. Kraczek, A. Janotti, T. C. Schulthess, G. M. Stocks, Duane D. Johnson
Duane D. Johnson
Ni/Fe/Co/Cu(100) films were epitaxially grown and investigated by photoemission electron microscopy. The magnetic correlation of the Ni and Co films was investigated by elementspecific domain images. We found that the Ni magnetization exhibits a continuous rotation in the spin reorientation transition (SRT) region and that the Ni SRT thickness oscillates with the Fe film thickness.
Reply To “Comment On ‘Classical Density Functional Theory Of Freezing In Simple Fluids: Numerically Induced False Solutions’ ”, M. Valera, F. J. Pinski, Duane D. Johnson
Reply To “Comment On ‘Classical Density Functional Theory Of Freezing In Simple Fluids: Numerically Induced False Solutions’ ”, M. Valera, F. J. Pinski, Duane D. Johnson
Duane D. Johnson
Recently we solved, via discrete numerical grids, the RamakrishnaYossouff densityfunctional theory equations for the freezing transition and obtained an intricate phase diagram of hardsphere mixtures. Even though such methods provide more variational freedom than basisset methods, we found that the thermodynamic quantities were sensitive to the spacing of numerical grids employed and observed numerically induced false minima. Dasgupta and Valls have commented that these false minima were due to our use of kspace methods and, hence, their early works based on a fully rspace approach are qualitatively correct, despite also being sensitive to the mesh granularity. Here, we clarify the ...
Absolute OrientationDependent Anisotropic Tin(111) Island Step Energies And Stiffnesses From Shape Fluctuation Analyses, S. Kodambaka, S. V. Khare, V. Petrova, Duane D. Johnson, I. Petrov, J. E. Greene
Absolute OrientationDependent Anisotropic Tin(111) Island Step Energies And Stiffnesses From Shape Fluctuation Analyses, S. Kodambaka, S. V. Khare, V. Petrova, Duane D. Johnson, I. Petrov, J. E. Greene
Duane D. Johnson
In situ hightemperature (1165–1248 K) scanningtunneling microscopy was used to measure temporal fluctuations about the anisotropic equilibrium shape of twodimensional TiN(111) adatom and vacancy islands on atomically smooth TiN(111) terraces. The equilibrium island shape was found to be a truncated hexagon bounded by alternating 〈110〉 steps, which form [100] and [110] nanofacets with the terrace. Relative step energies β as a function of step orientation φ were obtained from the inverse Legendre transformation of the equilibrium island shape to within an orientationindependent scale factor λ, the equilibrium chemical potential of the island per unit TiN area. We ...
Magnetochemical Origin For Invar Anomalies In IronNickel Alloys, V. Crisan, P. Entel, H. Ebert, H. Akai, Duane D. Johnson, J. B. Staunton
Magnetochemical Origin For Invar Anomalies In IronNickel Alloys, V. Crisan, P. Entel, H. Ebert, H. Akai, Duane D. Johnson, J. B. Staunton
Duane D. Johnson
Zero and finitetemperature (T) firstprinciples calculations versus composition (c) show that magnetochemical effects lead to Invar anomalies in Fe(Ni, Co, Pt) alloys. Chemical short or longrange order and negative interatomic exchange interaction of electrons in antibonding majorityspin states force the facecenteredcubic lattice to compete simultaneously for a smaller volume (from antiferromagnetic tendencies) and a larger volume (from Stoner ferromagnetic tendencies). The resulting additional negative lattice anharmonicity is very large for Fe(Ni, Co) while absent for FePt. Our results explain the T and cdependent behavior of Invar properties, including the lattice softening and thermal expansion of FeNi. In addition ...
Absolute Tin(111) Step Energies From Analysis Of Anisotropic Island Shape Fluctuations, S. Kodambaka, V. Petrova, S. V. Khare, Duane D. Johnson, I. Petrov, J. E. Greene
Absolute Tin(111) Step Energies From Analysis Of Anisotropic Island Shape Fluctuations, S. Kodambaka, V. Petrova, S. V. Khare, Duane D. Johnson, I. Petrov, J. E. Greene
Duane D. Johnson
In situ hightemperature (1165–1248 K) scanning tunneling microscopy was used to measure fluctuations around the equilibrium shape of twodimensional vacancy islands on TiN(111) terraces. From the equilibrium shape, the ratio of the two ⟨110⟩ step energies was found to be 0.72±0.02. Combining this with the results of an exact approach for analysis of shape fluctuations, applicable to highly anisotropic islands, we obtain absolute values for step energies and step stiffnesses as a function of orientation.
FirstPrinciples Theory Of The Temperature And Compositional Dependence Of Atomic ShortRange Order In Disordered CuPd Alloys, R. V. Chepulskii, J. B. Staunton, Ezio Bruno, B. Ginatempo, Duane D. Johnson
FirstPrinciples Theory Of The Temperature And Compositional Dependence Of Atomic ShortRange Order In Disordered CuPd Alloys, R. V. Chepulskii, J. B. Staunton, Ezio Bruno, B. Ginatempo, Duane D. Johnson
Duane D. Johnson
We combine the firstprinciples, KorringaKohnRostoker coherent potential approximation based calculations of compositional fluctuations with a statistical mechanical ring approximation to study the temperature (T) and composition (c) dependence of the atomic shortrange order (SRO) in disordered, facecentred cubic, CuPd alloys. The fourfold splitting of SRO peaks around the equivalent X(0,1,0) points in reciprocal space is obtained in a wide T−c region. Such splitting is shown to be an “energy” effect caused by the absolute minima of the Fourier transform of the effective atomic interactions and related previously to the existence of nested sheets of the disordered ...
Accuracy And Limitations Of Localized Green’S Function Methods For Materials Science Applications, Duane D. Johnson, Andrei V. Smirnov
Accuracy And Limitations Of Localized Green’S Function Methods For Materials Science Applications, Duane D. Johnson, Andrei V. Smirnov
Duane D. Johnson
We compare screened realspace and reciprocalspace implementations of KorringaKohnRostoker electronicstructure method for their applicability to largescale problems requiring various levels of accuracy. We show that realspace calculations in metals can become impractical to describe energies. We suggest a combined r and kspace scheme as the most efficient and flexible strategy for accurate energy calculations. Our hybrid code is suitable for (parallel) largescale calculations involving complex, multicomponent systems. We also discuss how details of numerical procedures can affect accuracy of such calculations.
Classical Density Functional Theory Of Freezing In Simple Fluids: Numerically Induced False Solutions, M. Valera, F. J. Pinski, Duane D. Johnson
Classical Density Functional Theory Of Freezing In Simple Fluids: Numerically Induced False Solutions, M. Valera, F. J. Pinski, Duane D. Johnson
Duane D. Johnson
Density functional theory (DFT) has provided many insights into the freezing of simple fluids. Several analytical and numerical solution have shown that the DFT provides an accurate description of freezing of hard spheres and their mixtures. Compared to other techniques, numerical, gridbased algorithms for solving the DFT equations have more variational freedom and are capable of describing subtle behavior, as that seen in mixtures with multipeaked density profiles. However the gridbased approach is sensitive to the coarseness of the mesh employed. Here we summarize how the granularity of the mesh affects the freezing point within the DFT. For coarse meshes ...
Unbiased Density Functional Solutions Of Freezing In Binary Mixtures Of Hard Or Soft Spheres, M. Valera, R. F. Bielby, F. J. Pinksi, Duane D. Johnson
Unbiased Density Functional Solutions Of Freezing In Binary Mixtures Of Hard Or Soft Spheres, M. Valera, R. F. Bielby, F. J. Pinksi, Duane D. Johnson
Duane D. Johnson
various size ratios, σ2/σ1, using density functional theory. The Grand Potential is minimized using an unbiased, discrete, realspace mesh that does not constrain the shape of the density, and, in many cases, leads to solutions qualitatively different from those using Gaussians and planewaves. Besides the usual facecenteredcubic solidsolution phase for σ2/σ1≈1.0, we find a sublatticemelt phase for σ2/σ1=0.85–0.5 (where the smallsphere density is nonlocalized and multipeaked) and the NaCl phase for σ2/σ1=0.45–0.35 (when the smallsphere density again sharpens). For a range of size ratios of soft ...
TemperatureInduced Configurational Excitations For Predicting Thermodynamic And Mechanical Properties Of Alloys, Duane D. Johnson, Andrei V. Smirnov, J. B. Staunton, F. J. Pinski, W. A. Shelton
TemperatureInduced Configurational Excitations For Predicting Thermodynamic And Mechanical Properties Of Alloys, Duane D. Johnson, Andrei V. Smirnov, J. B. Staunton, F. J. Pinski, W. A. Shelton
Duane D. Johnson
We show that a structural energy difference, ΔE, must include explicit symmetrybreaking changes of the electronic structure due to temperatureinduced configurational excitations, and why ΔE at T=0 K is not necessarily relevant to thermodynamic and mechanical modeling. In Ni3V, we calculate a tenfold decrease of ΔE between D022 and L12 structures from T=0 K to states of order relevant to experiment. ΔE calculated directly from states with shortrange order (8 meV) or with low partial order (7–12 meV) agree with highT experiment (10 meV).