Papers by Donald Nicholson
Parallel Processing for Scientific Computing, 1995
First principles methods are used to aid the material designers and metallurgists in the investig... more First principles methods are used to aid the material designers and metallurgists in the investigation and design of new materials. These methods suffer from a divergent O(N³) scaling which restricts the problem sizes that can be addressed. It will be demonstrated that the O(N³) scaling problem can be overcome by employing real-space multiple scattering techniques to calculate the scattering properties,
The spin moment distribution in magnetic nano-particles is both scientifically interesting and te... more The spin moment distribution in magnetic nano-particles is both scientifically interesting and technologically relevant. Here, we discuss the magnetic structure of FePt nano-particles, as determined by projector-augmented wave (PAW) and locally self-consistent multiple scattering (LSMS) local density calculations on nano-particles up to 3nm in size. The magnetic structure changes as a function of nano-particle size, composition, and chemical order, encompassing
Conference on High Performance Computing (Supercomputing), Nov 7, 1998
The understanding of metallic magnetism is of fundamental importance for a wide range of technolo... more The understanding of metallic magnetism is of fundamental importance for a wide range of technological applications ranging from thin film disc drive read heads to bulk magnets used in motors and power generation. In this submission for the Gordon Bell Prize we use the power of ...
International Journal of Quantum Chemistry, 1995
Using the concept of entangled states it is shown that density functional theory in its initial g... more Using the concept of entangled states it is shown that density functional theory in its initial ground-state formulationfootnotetextP. Hohenberg and W. Kohn, Phys. Rev. 136, B864, (1964).^,footnotetextW. Kohn and L. J. Sham, Phys. Rev. 140, A1133 (1965).^,footnotetextM. Levy, Proc. Nat. Acad. Sci. USA 76, 6062 (1979). is inherently capable of treating the excited states of interacting many-particle systems.footnotetextAcknowledgement: Discussions with
: This proceedings volume is a record of the third Materials Research Society symposium on High-T... more : This proceedings volume is a record of the third Materials Research Society symposium on High-Temperature Ordered Intermetallic Alloys. This volume also includes the paper 'Effect of Strain Rate on the Plastic Behavior of L(1,2) Compounds Based on Ni3AL. These proceedings demonstrate recent advances in understanding the physical metallurgy and mechanical properties of aluminides, silicides, and other intermetallics, with special emphasis on the beneficial effects boron additions on grain-boundary ductility of Li(1,2) compounds. Significant progress has also been made on processing and alloying of titanium aluminides with TiAL3, TiAL, and Ti3AL compositions. One session was devoted to alloy design and material processing, which aimed at improving mechanical and metallurgical properties of ordered intermetallic alloys. Because of recent growth of interest in multiphase intermetallic alloys, one session was also devoted to this area. Contents of this volume are broken down into t...
MRS Proceedings, 1988
ABSTRACTAt stoichiometry, DO22 is the observed ground state of Al2Ti and has a C/A ratio of 2.23,... more ABSTRACTAt stoichiometry, DO22 is the observed ground state of Al2Ti and has a C/A ratio of 2.23, but as a function of both concentration and temperature other ordered arrangements of APB's are observed. These phase transitions have sparked many studies in which the energy has been treated as that of chemical rearrangement on an fcc lattice. We have found that at the ideal C/A ratio, the Ll2 structure is lower in energy, but as the tetragonal distortion increases the DO22 energy drops below that of Ll2. The critical role played by the tetragonal distortion in the balance between Ll2 and DO22 energies precludes the use of any model based on the undistorted lattice.The major impediment to the development of Al3Ti as a high-temperature material is its lack of ductility. The standard approach is to make alloy additions which transform the structure to Ll2. An alternate approach is to work toward the enhancement of ductility in the DO22 phase. As a first step we have calculated the t...
scalable method for ab initio computation of free energies in
We review, briefly, the arguments which gave rise to the current controversy concerning the origi... more We review, briefly, the arguments which gave rise to the current controversy concerning the origin of compositional order in Ni{sub c}Pt{sub 1-c} alloys. We note that strain fluctuations play an important role in determining the state of compositional order in this system and outline a theoretical framework that takes account of them. 29 refs., 4 figs.
The continuous cooling transformation characteristics of novel bainitic steels have been studied,... more The continuous cooling transformation characteristics of novel bainitic steels have been studied, both under ordinary conditions and whilst subjected to a 30 T magnetic field. The magnetic field has been found to completely change the microstructure obtained, from a mixture of bainite and martensite to one containing an incredibly fine pearlite with an interlamellar spacing of about 50 nm. As a consequence, the pearlite is found to be much harder than any data found in the published literature.
Bulletin of the American Physical Society, 2010
We propose that within the class of pair potential Hamiltonians the excess entropy is a universal... more We propose that within the class of pair potential Hamiltonians the excess entropy is a universal, temperature-independent functional of the density and pair correlation. This result extends Henderson's Theorem which states that the free energy is a temperature dependent functional of the density and pair correlation. The stationarity and convexity of the excess entropy functional are discussed and related to
The electronic band structure of UNi2A13 and UPd2A13 is calculated in the local spin-density func... more The electronic band structure of UNi2A13 and UPd2A13 is calculated in the local spin-density functional approximation using the self-consistent scalar relativistic ASWmethod including spin-orbit coupling. The chemical bond is discussed qualitatively and an explanation is given for the small observed magnetic moments of U in terms of nearly compensating spin and orbital moments. Calculated total energies are used to discuss a number of possible ground state magnetic-moment configurations.
The continuous cooling transformation characteristics of novel bainitic steels have been studied,... more The continuous cooling transformation characteristics of novel bainitic steels have been studied, both under ordinary conditions and whilst subjected to a 30 T magnetic field. The magnetic field has been found to completely change the microstructure obtained, from a mixture of bainite and martensite to one containing an incredibly fine pearlite with an interlamellar spacing of about 50 nm. As a consequence, the pearlite is found to be much harder than any other examples found in the published literature.
The continuous cooling transformation characteristics of novel bainitic steels have been studied,... more The continuous cooling transformation characteristics of novel bainitic steels have been studied, both under ordinary conditions and whilst subjected to a 30 T magnetic field. The magnetic field has been found to completely change the microstructure obtained, from a mixture of bainite and martensite to one containing an incredibly fine pearlite with an interlamellar spacing of about 50 nm. As a consequence, the pearlite is found to be much harder than any data found in the published literature. Introduction Novel bainitic steels have recently been developed with strengths in excess of 2 GPa [1, 2, 3, 4]. The distinguishing characteristic of these steels is that they transform at such low temperatures that the bainite plates can be as thin as 20-40 nm; this, combined with the presence of carbonenriched austenite between the bainite ensures the impressive combination of strength and toughness [1-4]. This microstructure is generated during isothermal transformation at 200°C for more th...
We discuss methods which allow the determination of unique concentration dependent effective clus... more We discuss methods which allow the determination of unique concentration dependent effective cluster interactions (ECI's) in substitutional alloys. These methods are based on the coherent potential approximation (CPA) and on the representation of the configuration dependent part of the disorder energy in terms of ECI's. Two schemes proposed for calculating ECI's within the CPA framework, the generalized perturbation method (GPM) and the embedded cluster method (ECM) are compared with one another and with the method proposed by Connolly and Williams, both formally and by means of calculations. It is found that the GPM and the ECM are conceptually and numerically quite similar, the ECM corresponding to a complete summation of certain terms in the GPM expansion. Both these methods lead to unique values of ECI's for a large class of substitutional alloys, particularly strong-scattering alloys such as those involving transition metals. The Connolly-Williams approach, on t...
This document consists of equations for the electronic mean field theory, electronic grand potent... more This document consists of equations for the electronic mean field theory, electronic grand potential, Feynman-Pierles variational theorem, self-consistent KKR-CPa, KKR-CPA theory of direct correlation functions, first-principles Landau theory, and first-principles Cahn-Hilliard theory.
Journal of Applied Physics
High entropy alloys (HEAs), or concentrated solid solution alloys, are chemically complex metalli... more High entropy alloys (HEAs), or concentrated solid solution alloys, are chemically complex metallic solid solutions in which five or more elements occupy the same crystallographic lattice sites with nearly equal compositions. The high degree of chemical disorder gives rise to considerable local lattice distortions, atomic-level stresses, and complex electronic structure, resulting in interesting properties. We calculated the electronic structure and the atomic-level stresses of AlxTiyZryPdyCuyNiy, x = 0.5, y = 1 (Al0.5TiZrPdCuNi) HEA in the glassy phase using the density functional theory (DFT) approach. We also briefly discuss the electronic structure in its crystalline phase. Whereas it has been reported recently that the crystalline phase of this HEA is obtained as a metastable phase during the crystallization of a glassy phase, the crystalline phase was found to be unstable at T = 0 in the DFT calculation. For this reason, we focus mainly on the glassy phase in this work. The importance of charge transfer among elements on the atomic-level pressure and the role for atomic-level stresses to characterize the electronic and structural heterogeneity are discussed.
JOM, 2015
Abstract High-entropy alloys are multicomponent solid solutions in which various elements with di... more Abstract High-entropy alloys are multicomponent solid solutions in which various elements with different chemistries and sizes occupy the same crystallographic lattice sites. Thus, none of the atoms perfectly fit the lattice site, giving rise to considerable local lattice distortions and atomic-level stresses. These characteristics can be beneficial for performance under radiation and in a high-temperature environment, making them attractive candidates as nuclear materials. We discuss electronic origin of the atomic-level stresses based upon first-principles calculations using a density functional theory approach.
Journal of Physics and Chemistry of Solids, 2016
Density functional theory for the case of general, N-representable densities is reformulated in t... more Density functional theory for the case of general, N-representable densities is reformulated in terms of density functional derivatives of expectation values of operators evaluated with wave functions leading to a density, making no reference to the concept of potential. The developments provide proof of existence of a mathematical procedure that determines whether a density is vrepresentable and in the case of an affirmative answer determines the potential (within an additive constant) as a derivative with respect to the density of a constrained search functional. It also establishes the existence of an energy functional of the density that, for v-representable densities, assumes its minimum value at the density describing the ground state of an interacting many-particle system. The theorems of Hohenberg and Kohn emerge as special cases of the formalism. Numerical results for one-dimensional non-interacting systems illustrate the the formalism. Some direct formal and practical implications of the present reformulation of DFT are also discussed.
Uploads
Papers by Donald Nicholson