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Articles 1 - 15 of 15
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Systematic, Multisite Short-Range-Order 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 Short-Range-Order 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 Korringa-Kohn-Rostoker coherent-potential approximation (KKR-CPA) is used widely to configurationally average and get electronic structures and energies of disordered alloys, a single-site CPA misses local environment effects, including short-range order (SRO). A proposed nonlocal CPA (NLCPA) recovers translational invariance of the effective medium via k-space coarse graining from the dynamical cluster approximation (DCA), where corrections are systematic as cluster size increases. We implement a first-principles KKR-NLCPA/DCA and show the effects of environment, including SRO, on the electronic structures of fcc CuAu and bcc NiAl.
Scaling Relations For Dislocation Structure And Response, Richard Alan Lesar, M. Koslowski, Robb Thomson, J. M. Rickman
Scaling Relations For Dislocation Structure And Response, Richard Alan Lesar, M. Koslowski, Robb Thomson, J. M. Rickman
Richard Alan Lesar
A major goal in dislocation theory is the development of a coarse-grained method that would enable predictions of dislocation response without resolving the degrees of freedom of all the dislocations. While a number of possible coarse-grained theories have been proposed, all of these need information about structures at scales smaller than the coarse-graining volume. Here we present results from dislocation simulations that yield scaling relations with the hope that they can provide a framework for modeling the sub-scale dislocation structures and dynamics. For example, we show that dislocations have a self-similar (fractal) structure over wide range of stress/strain; dislocations move …
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 saddle-point barriers from only a few calculated points via molecular dynamics, thereby avoiding explicit calculation of all barriers. The GP-regressed barrier function enables use of kinetic Monte Carlo to simulate real-time kinetics (seconds to hours) based upon realistic atomic interactions. To illustrate the concept, we apply a GP regression to vacancy-assisted migration on a surface of a concentrated binary alloy (from both quantum and empirical potentials) and predict the diffusion …
Temperature Dependence Of Order, Disorder, And Defects In Laterally Confined Diblock Copolymer Cylinder Monolayers, Matthew R. Hammond, Eric W. Cochran, Glenn H. Fredrickson, Edward J. Kramer
Temperature Dependence Of Order, Disorder, And Defects In Laterally Confined Diblock Copolymer Cylinder Monolayers, Matthew R. Hammond, Eric W. Cochran, Glenn H. Fredrickson, Edward J. Kramer
Eric W. Cochran
Monolayer arrays of polystyrene-poly(2-vinylpyridine) diblock copolymer cylinders with excellent orientational order and a very low density of dislocations are prepared by cooling slowly from above the bulk order - disorder temperature (ODT) ∼212°C within silicon oxide channels one cylinder spacing a in depth and 2 μm in width. The translational order of this array, however, is short range with a correlation length of ∼12a. If such an array is heated to a temperature above the glass transition temperature of the block copolymer (100°C) but well below the ODT, a finite density of thermally generated dislocations is observed, which leads to …
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 I-Si(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 first-principles density functional theory, we determined the steric repulsive interactions associated with iodine and showed how the observed defect patterns …
Size-Driven Domain Reorientation In Hydrothermally Derived Lead Titanate Nanoparticles, Zhiyuan Ye, Elliot B. Slamovich, Alexander H. King
Size-Driven Domain Reorientation In Hydrothermally Derived Lead Titanate Nanoparticles, Zhiyuan Ye, Elliot B. Slamovich, Alexander H. King
Alexander H. King
High-resolution transmission electron microscopy studies of hydrothermally derived platelike lead titanate nanoparticles reveal that below a critical size of approximately 70 nm, the single ferroelectric domain polarization axis reorients from perpendicular to parallel to the plate. We suggest that during particle growth, ions in the hydrothermal processing medium compensate for the ferroelectric depolarization energy. When the processing medium is removed by washing and drying, single domain nanoparticles minimize their depolarization energy by c-axis flipping.
Theoretical Prediction Of New High-Performance Lead-Free Piezoelectrics, Pio Baettig, Charles F. Schelle, Richard Alan Lesar, Umesh V. Waghmare, Nicola A. Spaldin
Theoretical Prediction Of New High-Performance Lead-Free Piezoelectrics, Pio Baettig, Charles F. Schelle, Richard Alan Lesar, Umesh V. Waghmare, Nicola A. Spaldin
Richard Alan Lesar
We predict the occurrence of large ferroelectric polarization and piezoelectricity in the hypothetical perovskite-structure oxides, bismuth aluminate (BiAlO3) and bismuth gallate (BiGaO3), using density functional theory within the local density approximation. We show that BiGaO3 will have a similar structure to PbTiO3, although with much stronger tetragonal distortion and therefore improved ferroelectric properties. Likewise, BiAlO3 shares structural characteristics with antiferrodistortive PbZrO3, but it is also a ferroelectric with large polarization. Therefore, we propose the Bi(Al,Ga)O3 system as a replacement for the widely used piezoelectric material, Pb(Zr,Ti)O3 (PZT), that will avoid the environmental toxicity problems of lead-based compounds. Finally, we show …
Importance Of Thermal Disorder On The Properties Of Alloys: Origin Of Paramagnetism And Structural Anomalies In Bcc-Based 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 Bcc-Based 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 off-stoichiometric chemical disorder, and, although well studied, these properties are not understood. In stoichiometric B2 FeAl, including the effects of partial long-range 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 x≃0.25–0.5 under various …
Mechanism Of Structural Transformation In Bismuth Titanate, Sudhanshu Mallick, Keith J. Bowman, Alexander H. King
Mechanism Of Structural Transformation In Bismuth Titanate, Sudhanshu Mallick, Keith J. Bowman, Alexander H. King
Alexander H. King
Sodium-doped bismuth titanate undergoes a transformation from Bi4Ti3O12 to Na0.5Bi4.5Ti4O15 on heating in air at temperatures exceeding 800 °C. This transformation proceeds through the intermediate Na0.5Bi8.5Ti7O27 structure which is an intergrowth phase of the two. High-resolution transmission electron microscopy was used to study this transformation. From the Moiré pattern that was obtained, the crystallographic orientation of the transformation front has been determined and a mechanism is proposed for this structural transformation.
Inorganic Supramolecular Host Architectures: [(M@18c6)2][Tli4]·2h2o, M = 0.5 Tl, (Nh4,Nh3), (H3o,H2o), Franziska Rieger, Anja V. Mudring
Inorganic Supramolecular Host Architectures: [(M@18c6)2][Tli4]·2h2o, M = 0.5 Tl, (Nh4,Nh3), (H3o,H2o), Franziska Rieger, Anja V. Mudring
Anja V. Mudring
The compounds [(M@18c6)2][TlI4]·2H2O, M = Tl, (NH4,NH3), (H3O,H2O) (cubic, Fd3̄; a = 1481.00 pm, for M = 0.5 Tl, a = 1304.65 pm for M = (NH4,NH3), a = 1313.67 pm for M = (H3O,H2O)) can be obtained from solution in the presence of traces of transition metal halides (like copper and mercury halides). Apparently the transition metal cations work as a template in the form of tetrahedral [MX4] units during the synthesis of the supramolecular host architecture. That the compounds are versatile host lattices for tetrahedrally coordinated transition metal units becomes obvious by the large group of known host−guest …
The Quadrupole Moment Of The 3/2+ Nuclear Ground State Of Au197 From Electric Field Gradient Relativistic Coupled Cluster And Density-Functional Theory Of Small Molecules And The Solid State, Peter Schwerdtfeger, Radovan Bast, Michael C.L. Gerry, Christoph R. Jacobs, Martin Jansen, Vladimir Kello, Anja V. Mudring, Andrzej J. Sadlej, Trond Saue, Tilo Sohnel, Friedrich E. Wagner
The Quadrupole Moment Of The 3/2+ Nuclear Ground State Of Au197 From Electric Field Gradient Relativistic Coupled Cluster And Density-Functional Theory Of Small Molecules And The Solid State, Peter Schwerdtfeger, Radovan Bast, Michael C.L. Gerry, Christoph R. Jacobs, Martin Jansen, Vladimir Kello, Anja V. Mudring, Andrzej J. Sadlej, Trond Saue, Tilo Sohnel, Friedrich E. Wagner
Anja V. Mudring
An attempt is made to improve the currently accepted muonic value for the Au197 nuclear quadrupole moment [+0.547(16)×10−28m2] for the 3/2+ nuclear ground state obtained by Powers et al. [Nucl. Phys.A230, 413 (1974)]. From both measured Mössbauer electric quadrupole splittings and solid-state density-functional calculations for a large number of gold compounds a nuclear quadrupole moment of +0.60×10−28m2 is obtained. Recent Fourier transform microwave measurements for gas-phase AuF, AuCl, AuBr, and AuI give accurate bond distances and nuclear quadrupole coupling constants for the Au197isotope. However, four-component relativistic density-functional calculations for these molecules yield unreliable results for the Au197 nuclear quadrupole moment. …
Rare-Earth Iodides In Ionic Liquids: The Crystal Structure Of [Set3]3[Lni6] (Ln = Nd, Sm), Anja V. Mudring, Arash Babai
Rare-Earth Iodides In Ionic Liquids: The Crystal Structure Of [Set3]3[Lni6] (Ln = Nd, Sm), Anja V. Mudring, Arash Babai
Anja V. Mudring
Crystals of [SEt3]3[LnI6] (Ln = Nd, Sm) were obtained by the reaction of LnI2 with the ionic liquid [SEt3][Tf2N] [Tf2N = bis(trifluoromethanesulfonyl)imide]. The compounds are characterized by octahedral [LnI6]3- units that are surrounded by a distorted cube of triethylsulfonium cations.
Dislocation-Indenter Interaction In Nanoindentation, M. Ravi Shankar, Alexander H. King, Srinivasan Chandrasekar
Dislocation-Indenter Interaction In Nanoindentation, M. Ravi Shankar, Alexander H. King, Srinivasan Chandrasekar
Alexander H. King
A formulation of dislocation-indenter interaction in two-dimensional, isotropic elasticity is presented. A significant dislocation-indenter interaction is predicted when dislocations are nucleated very close to the indenter. This interaction is expected to have an important influence on dislocation motion and multiplication. Upon nucleation close to the indenter, the dislocations are shown to modify the load, load distribution, and moment acting on the indenter. This effect is seen to vary with the indentation contact length. Further away from the indenter, the indenter-dislocation interaction is shown to be negligible.
Anhydrous Praseodymium Salts In The Ionic Liquid [Bmpyr][Tf2n]: Structural And Optical Properties Of [Bmpyr]4[Pri6][Tf2n] And [Bmyr]2[Pr(Tf2n)5], Arash Babai, Anja V. Mudring
Anhydrous Praseodymium Salts In The Ionic Liquid [Bmpyr][Tf2n]: Structural And Optical Properties Of [Bmpyr]4[Pri6][Tf2n] And [Bmyr]2[Pr(Tf2n)5], Arash Babai, Anja V. Mudring
Anja V. Mudring
Purposely designed ionic liquids can be excellent solvents for spectroscopic studies of rare earth compounds. Absorption and emission spectra of anhydrous PrI3 and Pr(Tf2N)3 in the ionic liquid 1,1-n-butyl-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide, [bmpyr][Tf2N], at room temperature are presented together with the emission spectra of solid [bmpyr]2[Pr(Tf2N)5] and [bmpyr]4[PrI6][Tf2N]. After excitation into the 3P1 level, remarkable luminescence not only from the 1D2 level but also from the 3P0 and even from the 3P1 level is observed. Amazingly in the case of the solid compounds and even more astonishing for a solution of Pr(Tf2N)3 in [bmpyr][Tf2N] the strongest luminescence transitions start from the 3P0 …
Lone Pair Effect In Thallium(I) Macrocyclic Compounds, Anja V. Mudring, Franziska Rieger
Lone Pair Effect In Thallium(I) Macrocyclic Compounds, Anja V. Mudring, Franziska Rieger
Anja V. Mudring
The role of the inert (lone) pair of electrons in thallium(I) salts is studied by comparison of the compounds [Tl@18-crown-6]+X- (X = TlI4, ClO4) and [K@18-crown-6]+ClO4-. In contrast to common introductory chemistry textbook opinions, the paradigm that s−p hybridization is a prerequisite for an inert electron pair to become stereochemically active in compounds of the heavier main group elements has to be revised. Instead, an inert pair of electrons is expected to become stereochemically involved whenever it is forced to participate in antibonding orbital interactions with its surroundings, and there is the possibility for a structural distortion that minimizes these …