Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session X28: Electronic Theory of Metals |
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Sponsoring Units: DMP Chair: Don Nicholson, ORNL Room: LACC 506 |
Friday, March 25, 2005 8:00AM - 8:12AM |
X28.00001: Anomalous Hall effect and the ``quantum geometry'' of the Fermi surface of metals in Fermi liquid theory. F.D.M. Haldane The ``anomalous Hall effect'' in ferromagnetic metals was recently found to be a previously-unrecognized fundamental Fermi liquid property (FDMH, Phys. Rev. Lett. {\bf 96}, 203602 (2004)), arising from the Berry curvature of the quasiparticle Bloch state at the Fermi surface, when time-reversal symmetry is broken. This turns out to be a fundamental property of metallic Fermi liquids that survives the ``switching on'' of interactions, protected by Ward identities. The Fermi surface is not just a 2-manifold embedded in k-space, but also a 2-manifold embedded in the Hilbert space describing the periodic factor in the quasiparticle Bloch state. Both embeddings induce geometry: the second embedding not only induces a U(1) or SU(2) gauge (Berry) connection, but also a second Riemannian structure. The new realization that the periodic Bloch factor (plus the spin state) induces an extra ''quantum geometry'' of the Fermi surface points towards a new topological description of Fermi liquid theory. Explicit formulas for the anomalous Hall conductivity, Drude tensor, and other properties of arbitary-shape Fermi surfaces will be reviewed. Separate adiabatic conservation laws are associated with each distinct Fermi surface manifold: this generalizes the separate conservation laws at each Fermi point in 1D Luttinger liquids. [Preview Abstract] |
Friday, March 25, 2005 8:12AM - 8:24AM |
X28.00002: Hartree-Fock theory of a current-carrying electron gas H\'{e}ctor Mera, Rex Godby, Peter Bokes State-of-the-art simulation tools for non-equilibrium quantum transport systems typically describe the current-carrier occupations in terms of the equilibrium distribution functions of two particle reservoirs characterized by two different electrochemical potentials, while for the description of electronic exchange and correlation, the Local Density Approximation (LDA) to Density Functional Theory is generally used. However, the LDA is based on the homogeneous electron gas \emph{in equilibrium} and therefore its use is inconsistent with the non-equilibrium character of the system to be described. In this work we remove this inconsistency by maximizing the entropy of a two dimensional electron gas with constraints on the total energy and number of left- and right-going electrons and solving the corresponding Hartree-Fock equations. We find that the exchange energy depends only weakly on the current density despite quite considerable changes in the single particle spectrum. This is explained in terms of the symmetries of the exchange hole and its dependence on the current density. Consequences for a current-dependent LDA to the exchange potential are also discussed. [Preview Abstract] |
Friday, March 25, 2005 8:24AM - 8:36AM |
X28.00003: Chiral spin resonance and spin-Hall conductivity in the presence of the electron-electron interactions. Arcadi Shekhter, Maxim Khodas, Alexander Finkel'stein We discuss the electron spin-resonance in 2D electron gas at zero external magnetic field. This spin-resonance is due to the transitions between the electron states, which are split by the spin-orbit (SO) interaction, and is termed as the chiral spin resonance (CSR). It can be excited by the in-plane component of the electric field of the microwave radiation. We show that there exists an inherent relationship between the spin-Hall conductivity and the CSR in a system with the SO interaction. Since in the presence of the SO interaction spin is not conserved, the electron-electron interaction renormalizes the spin-Hall conductivity as well as the frequency of the CSR. The effects of the electron interaction in systems with the SO interaction are analyzed both phenomenologically and microscopically. [Preview Abstract] |
Friday, March 25, 2005 8:36AM - 8:48AM |
X28.00004: First-principles calculation of impurity diffusion barriers in Al Nils Sandberg, Randi Holmestad We have performed extensive electronic structure calculations to obtain impurity$+$vacancy formation energies, $H_{\rm iv}$, and impurity migration energies, $H_{\rm im}$, in Al matrix. The impurities considered are Mg, Si and the 3d transition metals (Sc-Zn). We have also estimated the correlation factor $f$, accounting for the `non-randomness' of successive impurity migration jumps. The total effective impurity diffusion barriers $H_{\rm iD}=H_{\rm iv}+H_{\rm im}- {\rm d} \ln (f)/{\rm d}(1/k_{\rm B}T)$ compare well with experimentally measured diffusion barriers (see, e.g., evaluation in Du et al, Mater. Sci. Eng. A {\bf 363}, 140 (2003)). $H_{\rm iD}$ varies strongly over the 3d series transition metals, mainly due to a strong variation in the migration barrer $H_{\rm im}$, which explains why, e.g., Mn diffuses orders of magnitude slower than, e.g., Al (self diffusion). Mg, Si Zn and Cu are found to be fast diffusers compared to Al. Two main sources of error on the theory side are a) temperature dependencies in $H_{\rm iv}$ and $H_{\rm im}$ due to anharmonicity in the atomic vibrations and b) the choice of exchange-correlation approximation. Both these factors will be discussed. [Preview Abstract] |
Friday, March 25, 2005 8:48AM - 9:00AM |
X28.00005: Pressure dependence of the ideal tensile strength of bcc niobium Weidong Luo, Marvin L. Cohen, J. W. Morris, Jr. The pressure dependence of the ideal tensile strength of bcc niobium was investigated using the {\it ab initio} pseudopotential density-functional method. The external stress is applied perpendicular to the main tensile strain direction. With positive external stress, the stresses of both the tetragonal Bain path and the orthorhombic path move up to higher values, resulting in higher ideal tensile strength. Also, the branching of these two paths moves out to higher strain. With negative (compressive) external stress, the ideal tensile strength decreases, and the branching of the orthorhombic path and tetragonal path moves to smaller strain. The change in the ideal tensile strength can be explained using simple arguments. [Preview Abstract] |
Friday, March 25, 2005 9:00AM - 9:12AM |
X28.00006: Extraction of an effective pair potential from a many body potential of metallic systems Xueyu Song, Tomaz Urbic, Vadim Warshavsky, Cai-Zhuang Wang For metallic systems most reliable descriptions are given by many body potentials and on the other hand most of successful liquid theories are formulated based upon pair potentials. The effective state-dependent pair intermolecular potential can be calculated as a solution of the modified hypernetted chain (MHNC) integral equation. With an initial guess of the bridge function in this equation either from the conventional MHNC approximation [1] or from the Fundamental Measure Density Functional Theory [2] several iterations with simulations lead to converged pair potential [3]. In this report we use the both methods to extract an effective pair potential from an embedded atom model potential of aluminum and a tight-binding many-body potential of silicon [4]. Using the effective pair potential the calculated phase diagrams agrees well with the phase diagram from direct simulations via the original many body potential. 1. Y.Rosenfeld and N.W.Ashcroft, Phys.Rev.A 20, 1208(1979). 2. Y.Rosenfeld and G.Kahl, J.Phys.:Condens.Matter 9, L89(1997). 3. L.Reatto, D.Levesque and J.J.Weis, Phys.Rev.A, 33, 3451(1986). 4. C.Z.Wang, B.C.Pan, and K.M.Ho, J. Phys. : Condens. Matter 11, 2043 (1999). [Preview Abstract] |
Friday, March 25, 2005 9:12AM - 9:24AM |
X28.00007: First Principles Predictions of Unsuspected Ordered Structures in Au-Pd fcc Alloys Sergey V. Barabash, Volker Blum, Alex Zunger, Stefan M\"uller Experimentally, the phase diagram of Au-Pd shows only a disordered solid solution, but even though $\Delta H < 0$, no ordered bulk phases have yet been detected. To find what are the ordered structures at lower temperatures, we perform a mixed-basis cluster expansion of $T=0$ and finite $T$ properties of Au-Pd fcc alloys. Starting from {\em ab- initio} data, and using genetic algorithm to select most relevant figures, we build a cluster expansion able to predict total energies of arbitrary lattice configuration with precision comparable to that of ab-initio calculations themselves. We predict many unusual low-temperature ground state structures for bulk Au-Pd alloys. In particular, at $x=0.5$, we predict Kanamori's structure ``40'' (common in zincblende semiconductors yet extremely rare in metallic alloys). At both $x=0.25$ and $x=0.75$, we find tendencies for forming L1$_2$-based superstructures, however the energetic competition between such structures is different at the two compositions, which imposes specific requirements on the properties of the cluster expansion Hamiltonian. Having met those requirements, we are able to further predict novel ground state structures in the Au-rich region of the phase diagram. The stability of those compounds at finite temperatures, their ordering temperatures, the short-range order and the properties of the random alloy are analyzed. [Preview Abstract] |
Friday, March 25, 2005 9:24AM - 9:36AM |
X28.00008: Study of the ideal strength and electronic structure in B2 transition-metal aluminides Tianshu Li, J.W. Morris, Jr., D.C. Chrzan The ideal tensile and shear strengths of the B2-type (CsCl) transition-metal aluminides FeAl, CoAl, and NiAl have been investigated systematically using an \textit{ab initio} electronic structure total energy method. Our calculation explains the unique weakness in FeAl under the $\langle 100 \rangle$ uniaxial tension as compared to NiAl, in which the shear instability intrudes before it approaches the tensile instability at a large critical strain. The weakness of FeAl along $\langle 001\rangle$ direction is attributed to an instability introduced by the filling of antibonding $d$ states. The calculation thus provides a theoretical basis for the observed cleavage behavior of the three materials. This work is supported by Department of Energy, Basic Energy Sciences under the Office of Science under contract DE-AC03-76SF00098. [Preview Abstract] |
Friday, March 25, 2005 9:36AM - 9:48AM |
X28.00009: New Class of Mn Based MAX Phases Sa Li, Puru Jena, Rajeev Ahuja The MAX phase materials are a class of ternary compounds with formula unit: M$_{N+1}$AX$_{N}$ (MAX), where N = 1, 2 or 3, M is an early transition metal, A is an A-group (mostly IIIA and IVA) element, and X is either C and/or N. These ternary carbides and nitrides combine unusual properties of both the metals and ceramics. They exhibit high hardness, but fully reversible plasticity, and negligible thermoelectric power. In this paper, we report a new series of MAX phases which not only possess the usual properties of the MAX phase, but also are magnetic under ambient conditions. The electronic structure and magnetic properties of Mn based MAX phases have been systematically studied by means of first principles method based on the density functional theory. By comparing the energy difference between the ferromagnetic and antiferromagnetic configurations for the Mn based MAX phases, we determined that there are one Mn$_{2}$(Al, Si)X phase, two Mn$_{3}$(Al, Si)X$_{2}$ phases, and three Mn$_{4}$(Al, Si)X$_{3 }$phases which can be stabilized in the ferromagnetic state. This finding adds a new property to the MAX phase materials for technological applications. [Preview Abstract] |
Friday, March 25, 2005 9:48AM - 10:00AM |
X28.00010: Systematically exact corrections from multisite configurations on the electronic structure of disordered alloys Dominic Biava, Subhradip Ghosh, Duane D. Johnson, William A. Shelton, A. V. Smirnov The Korringa-Kohn-Rostoker coherent-potential approximation (KKR-CPA) is widely used to study electronic structure and energy of disordered alloys, but the single-site CPA is missing effects from the local environment, including short-range order. A cluster-based \emph{non-local} CPA (NLCPA) was proposed that recovers the translational-invariance of the medium from reciprocal-space coarse-graining used in the dynamical cluster approximation (DCA), where corrections are casual and systematic as the cluster size increases. We implemented a first-principles KKR-NLCPA/DCA and study the effect of local environment, including short-range order, on the electronic structure of fcc $CuAu$ and bcc $NiAl$. [Preview Abstract] |
Friday, March 25, 2005 10:00AM - 10:12AM |
X28.00011: Importance of the 5$f$-Pseudopotential for 5$d$ Transition Metals Nichols Romero, Nithaya Chetty, Richard Martin It is usual to neglect the $\ell=3$ component of the pseudopotential (PP) in {\it ab initio} density functional calculations of 5$d$ transition metals. In most of these elements, the 5$f$ orbitals are unbound in the neutral ground-state configuration of the atom. We construct the 5$f$-PP using the Hamman procedure for unbound states [1], and carry out planewave (PW) calculations using ABINIT [2] for selected 5$d$ transition metals. We show that omission of the 5$f$-PP leads to systematic errors in the bulk properties for some elements. Although all-electron (AE) methods are often used for studying these materials in bulk, the PP-PW method is computational less expensive by comparison and can be readily used to study complicated geometries like surfaces. The 5$d$ transition metals are important elements because they form stable hard materials. For example, iridium is used in the calibration of high pressure diamond anvils because of its extreme stability at high pressure and temperature. [1] D. R. Hamann, Phys. Rev. B 40 2980 (1989). [2] X. Gonze et. al, Comp. Mat. Sci. 25, 478 (2002). [Preview Abstract] |
Friday, March 25, 2005 10:12AM - 10:24AM |
X28.00012: Ab-initio Calculations for MEAM Potential of Al, Si, Mg, H, O and Cu Alloys Bohumir Jelinek, Seong-Gon Kim, Mark Horstemeyer, Michael I. Baskes The ab-initio calculations based on the density functional theory (DFT) were performed for the Si, Al, Mg, H, O, Cu crystals and their pair combinations in reference structures, such as NaCl structure. The lattice constant (volume), bulk modulus and shear moduli for each pair were determined from the total energy calculations. These material parameters were then used to determine the Modified Embedded Atom Method (MEAM) potentials for these elements and their alloys. MEAM simulations that model the mechanical properties of these alloy materials will be presented to demonstrate the validity and transferability of the new MEAM potentials. [Preview Abstract] |
Friday, March 25, 2005 10:24AM - 10:36AM |
X28.00013: Absence of metastable states in strained monoatomic cubic crystals. Aar{\'o}n Aguayo, Michael L. Mehl, L.L. Boyer, Romeo de Coss The Bain path distortion of a metal with an fcc (bcc) ground state toward the bcc (fcc) structure initially requires an increase in energy, but at some point along the Bain path the energy will again decrease until a local minimum is reached. We have studied the tetragonal distortion (Bain path) of monoatomic cubic crystals, using a combination of parametrized tight-binding and first-principles linearized augmented plane wave calculations. We show that this local minimum is unstable with respect to an elastic distortion, except in the rare case that the minimum is at the bcc (fcc) point on the Bain path. This shows that body-centered-tetragonal phases of these materials, which have been seen in epitaxially grown thin films, must be stabilized by the substrate and cannot be freestanding films. This work was partially supported by Consejo Nacional de Ciencia y Tecnolog{\'\i}a (CONACYT, M{\'e}xico) under Grant No. 43830-F. [Preview Abstract] |
Friday, March 25, 2005 10:36AM - 10:48AM |
X28.00014: NRL Tight-Bindind Model for Alkali Metals Lei Shi, Dimitrios Papaconstantopoulos We have extended our studies with the NRL tight-binding method to the alkali metal column of the periodic table. The method was applied to Potassium, Rubidium and Cesium. We fit APW calculations of high symmetry structures onto a non-orthogonal tight-binding Hamiltonian. This Hamiltonian accurately reproduces the APW band structures, density of states and total energies as a function of volume. In addition, the tight- binding scheme determines various quantities that were not fitted, such as elastic constants, phonon frequencies and vacancy formation energy in agreement with experimental values. We explore the applicability of this model in performing molecular dynamics simulations. In addition, we will provide comparison with a recent improvement to Harrison's tight- binding theory[1]. [1]Lei Shi and Dimitrios A. Papaconstantopoulos, Phys. Rev. B, 70, 205101(2004). [Preview Abstract] |
Friday, March 25, 2005 10:48AM - 11:00AM |
X28.00015: Tight-binding calculations of the band structure and phases of Zinc and Cadmium Christopher Ashman, Dimitris Papaconstantopoulos, Michael Mehl Tight-binding calculations for Zn and Cd in a variety of crystal structures have been examined using the NRL non-orthogonal tight-binding model with parameters selected to accurately fit the first-principles results. These parameters correctly predict hcp to be the stable crystal structure for both Zn and Cd and reproduce well the first-principles band structure. We have calculated other properties, which were not included in the fit, such as elastic constants, bulk phases, the vacancy formation energy and phonon frequencies. We find good agreement with available calculations and experiment. [Preview Abstract] |
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