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Efficient solution of the relativistic APW secular equation for both eigenvalues and eigenvectors

Description: From international symposium on atomic, molecular, solidstate theory, and quantum statistics: Sanibel Island, Florida, USA (20 Jan 1974). The special problems introduced into the solution of the secular equation by the inclusion of relativistic effects are discussed. A method based on the use of linear combination of RAPW's is then described for solving the secular equation. This method greatly reduces the computer time and core space required to solve the secular problem and is particularly advantageous in large systems. (auth)
Date: January 1, 1974
Creator: Koelling, D.D.
Partner: UNT Libraries Government Documents Department

Band description of materials with localizing orbitals

Description: Density functional theory is a form of many-body theory which maps the problem onto an equivalent single particle-like system by limiting to the ground state (or some limited ensemble). So it should be surprising that this ground state theory could have any relevance whatsoever to the excitation properties of a material - and yet it does when used carefully. However, the most interesting materials involve active orbitals which are at least partially localized in space and this has profound effects both on the ground state and the excitation spectrum. My long term interest is in Ce and actinide compounds such that the popular concerns are mixed valence, heavy fermions, and the various forms of magnetic transitions. Band structure calculations can give a great deal of information concerning the mechanisms and degree of the localization as shown by examples using the Ce and U Ll/sub 2/ structured materials and the Ce cubic Laves phase materials. There are some difficulties due to an incomplete knowledge of the functionals involved which causes an underestimate of the local character. This is illustrated and discussed.
Date: March 1, 1986
Creator: Koelling, D.D.
Partner: UNT Libraries Government Documents Department

Band theory approach for actinides

Description: The application of band theory to actinide systems is investigated. The fundamental aspects are considered to define the limits of applicability. The more practical approximate applications are then considered to demonstrate their underlying assumptions and range of applicability. Examples are drawn primarily from our own work on Th ..cap alpha..-U and UGe/sub 3/.
Date: January 1, 1978
Creator: Koelling, D.D.
Partner: UNT Libraries Government Documents Department

Band model for d- and f-metals

Description: The application of band theory to metallic systems with d- and f-orbitals in the valence and conduction bands is discussed. Because such an application pushes theory and technique to their limits, several important features are briefly recapitulated. Within the transition metal systems, the elemental systems are used to discuss the fundamental formalism being applied and the newer directions into more complex systems are mentioned. Here we focus more on anisotropic properties and Fermi surface properties. Within the f-orbital systems, the focus is more on Ce and its compounds because of current interest with a relatively brief discussion of the actinides. the point of view advanced, however, has its origins in actinide research.
Date: January 1, 1982
Creator: Koelling, D.D.
Partner: UNT Libraries Government Documents Department

F-electron systems: Pushing band theory

Description: The f-electron orbitals have always been the incomplete atomic shell acting as a local moment weakly interacting with the remaining electronic structure'' in the minds of most people. So examining them using a band theory where one views them as itinerant once was -- and to some extent even today still is -- considered with some skepticism. Nonetheless, a very significant community has successfully utilized band theory as a probe of the electronic structure of the appropriate actinides and rare earths. Those people actually using the approach would be the first to declare that it is not the whole solution. Instead, one is pushing and even exceeding its limits of applicability. However, the appropriate procedure is to push the model consistently to its limits, patch where possible, and then look to see where discrepancies remain. I propose to offer a selected review of past developments (emphasizing the career to date of A. J. Freeman in this area), offer a list of interesting puzzles for the future, and then make some guesses as to the techniques one might want to use. 27 refs.
Date: August 1, 1990
Creator: Koelling, D.D.
Partner: UNT Libraries Government Documents Department

Electronic energy band structure of actinide metals and intermetallics

Description: The behavior of the 5f electrons as the crucial factor in determining the electronic properties of materials containing actinides is discussed. Whether these electrons will be localized or itinerant depends on the relative size of the Coulomb correlation and the near-neighbor interaction (bandwidth) terms. Evidence from optical reflectivity and de Haas-van Alphen measurements which show that the f-states are itinerant in the light actinide metals is examined. The mechanisms by which this occurs are studied and it is shown that the dominant feature is a direct f-f interaction on neighboring sites. It is as a result of this dominance that correlations with actinide separation are found for the observed superconducting and magnetic properties. Since materials which appear as exceptions to this correlation are significant as systems where the direct f-f interaction is not the dominant term, we discuss, as illustrative examples, the L1$sub 2$ crystal structure materials involving uranium. The materials considered in detail are URh$sub 3$ and UIr$sub 3$ for which an experimental determination of the Fermi surface has been made. In these systems, the dominant interaction is found to be the formation of a d-f bond. (auth)
Date: January 1, 1975
Creator: Koelling, D.D. & Freeman, A.J.
Partner: UNT Libraries Government Documents Department

Analysis of the series of moderately heavy fermion materials: CeSn/sub 3/, USn/sub 3/, and NpSn/sub 3/

Description: The materials CeSn/sub 3/, USn/sub 3/, and NpSn/sub 3/ are all moderately heavy Fermion compounds with electronic specific heat coefficients of 73, 169, and 242 mJ/mole K/sup 2/. CeSn/sub 3/ is known as a mixed valent system and NpSn/sub 3/ is a weak itinerant antiferromagnet. All three are strongly enhanced. Being in the relatively simple Au/sub 3/Cu structure, they form an excellent set of materials to study as representatives of strongly enhanced systems. One would like to ascertain what properties can be determined from band calculations based on density functional theory in the local density approximation. It has already been shown that the Fermi surface topology of CeSn/sub 3/ can be well described in this way even though the experimental masses are much larger than the band results. The enhancement factor for USn/sub 3/ is even larger and NpSN/sub 3/ is indeed predicted to go magnetic. We present here fully relativistic SCF calculations for these materials and discuss the relation between our results and what is known experimentally.
Date: May 1, 1985
Creator: Norman, M.R. & Koelling, D.D.
Partner: UNT Libraries Government Documents Department

Magnetic ordering and electronic structure of CeAl/sub 2/

Description: CeAl/sub 2/ has attracted considerable attention because of its unusual properties including a proposed competition between Kondo and anti=ferromagnetic spin-density wave ordering observed at low temperatures. Here we present results of a self-consistent spin-polarized linear muffin tin orbital band study of CeAl/sub 2/. In its paramagnetic state the Ce-f band is about 1 eV wide and, although principally above E/sub F/, it accommodates the additional 4f electron when compared to LaAl/sub 2/ and gives rise to a very high DOS at E/sub F/. The ferromagnetic state is found not to be stable. By contrast, the anti-ferromagnetic state is found to be stable with a magnetic moment of 0.88..mu../sub B/ per Ce atom in very good agreement with neutron measurements by Barbara et al. Surprisingly, the anti-ferromagnetic spin-density ordering appears to be related to nesting features in the underlying Fermi surface in LaAl/sub 2/ (i.e., no 4f electron) rather than that of CeAl/sub 2/.
Date: January 1, 1982
Creator: Jarlborg, T.; Freeman, A.J. & Koelling, D.D.
Partner: UNT Libraries Government Documents Department

Magnetic properties and electronic structure of the actinide systems UAl/sub 2/, NpAl/sub 2/, and PuAl/sub 2/

Description: The electronic ground states of UAl/sub 2/, NpAl/sub 2/ and PuAl/sub 2/ have been determined by band theory techniques. These calculations indicate that both actinide d-f hybridization and spin-orbit coupling are important in these systems. Using a new scheme for obtaining the paramagnon parameters for UAl/sub 2/ it is shown that calculated and experimentally derived 5f band width are consistent. The fact that orbital angular momentum may not be quenched in these systems is suggested as a possible mechanism for damping spin-fluctuations in NpAl/sub 2/ and PuAl/sub 2/.
Date: January 1, 1985
Creator: Albers, R.C.; Boring, A.M. & Koelling, D.D.
Partner: UNT Libraries Government Documents Department

5f-band narrowing in UX/sub 3/B compounds: evidence from resonant photoemission. [X = Ru or Rh]

Description: Resonant photoemission at the uranium 5d disorption edge has been used to determine the 5f emission in URu/sub 3/, URh/sub 3/, URu/sub 3/B, and URh/sub 3/B polycrystalline samples. The observed 5f band narrowing (from 2.0 to 1.5 eV as one goes from URu/sub 3/ to URu/sub 3/B, and from 2.8 to 1.1 eV for URh/sub 3/ and URh/sub 3/B respectively) is explained as due to a decrease in the f-d hybridization between uranium and rhodium (ruthenium) atoms.
Date: October 1, 1985
Creator: Zolnierek, Z.; Arko, A.J. & Koelling, D.D.
Partner: UNT Libraries Government Documents Department

Band structure of UO/sub 2/: an angle resolved and resonant photoemission study

Description: A detailed study of angle resolved photoemission of UO/sub 2/ <100> in the normal emission configuration is presented. The results are compared to a semirelativistic LAPW band calculation with the actual calculated empty bands used in the data reduction. Excellent agreement is found with calculations both for filled states as well as critical points in the empty states with no adjustment of bands. f-p hybridization is found at the leading edge of the valence band and not at the bottom of the valence band. p-d hybridization is found throughout the valence bands.
Date: October 1, 1985
Creator: Arko, A.J.; Koelling, D.D.; Boring, A.M.; Ellis, W.P. & Cox, L.E.
Partner: UNT Libraries Government Documents Department

Observation of high field DHVA-effect and induced magnetism in single crystal TiBe/sub 2/

Description: Recently much interest has been given to itinerant magnetism in cubic Laves phase or C15 materials. Primarily this stems from the discussion of the relationship of p-state pairing and ferromagnetism in ZrZn/sub 2/ by Enz and Matthias, and the possibility of triplet superconductivity. The most recent work in this field has focused on the isoelectronic, isostructural material TiBe/sub 2/, and the possibility that this material is metamagnetic. That TiBe/sub 2/ is close to some form of magnetic instability can be infered indirectly from the peaked nature of its density of states near the fermi level, but also from the observation of ferromagnetism in TiBe/sub 2-x/Cu/sub x/, when x is greater than about 0.15. In this paper a single crystal of pure TiBe/sub 2/ is considered in fields larger than 15 Tesla (T) and at a temperature of 1.3/sup 0/K.
Date: January 1, 1981
Creator: van Deursen, A.P.J.; van Ruitenbeek, J.M.; Verhoef, W.A.; de Vroomen, A.R.; Smith, J.L.; de Groot, R.A. et al.
Partner: UNT Libraries Government Documents Department

Is YbAs a heavy Fermion system

Description: Using parameters extracted from a tight binding fit to an ab initio band structure, the specific heat anomaly observed in YbAs around 5 K is computed within the infinite U limit of the degenerate Anderson impurity model. Applying the renormalization procedure derived in variational treatments of the periodic Anderson model, a quasiparticle Fermi surface with strong nesting features and small mass enhancements is obtained. The results suggest that YbAs is not a classical'' heavy Fermion system. 28 refs., 3 figs., 1 tab.
Date: August 1, 1989
Creator: Monnier, R.; Degiorgi, L.; Delley, B.; Koelling, D.D. (Eidgenoessische Technische Hochschule, Zurich (Switzerland). Lab. fuer Festkoerperphysik; Paul Scherrer Inst. (PSI), Villigen (Switzerland) & Argonne National Lab., IL (USA))
Partner: UNT Libraries Government Documents Department

Electronic structure studies of YBa{sub 2}Cu{sub 3}O{sub x}(6.2 {le} x {le} 6.9) using angle resolved photoemission

Description: Using high resolution angle resolved photoemission, the electronic structure of YBa{sub 2}Cu{sub 3}O{sub x} is examined when oxygen stoichiometries are varied in the range 6.2 {le} {times} {le} 6.9. Detailed measurements of the Fermi surface for YBa{sub 2}Cu{sub 3}O{sub 6.9} are presented and are compared with predictions of band theory. In the metallic region of the phase diagram, changes in the Fermi surfaces are measured as a function of oxygen stoichiometry. The electronic structure is monitored as the oxide changes from a metal to a semiconductor with additional oxygen depletion. For intermediate stoichiometries, effects of oxygen vacancy ordering are considered. Unusual resonant effects observed at several photon energies are examined as oxygen content is varied.
Date: November 1, 1992
Creator: Veal, B. W.; Liu, Rong; Paulikas, A. P.; Koelling, D. D.; Downey, J. W.; Shi, Hao et al.
Partner: UNT Libraries Government Documents Department

Understanding photoemission spectra in uranium based heavy fermion systems

Description: In 4f compounds, there is a two-peaked structure associated with 4f photoemission spectroscopy, while most 5f compounds yield a single broad triangular-shaped 5f intensity. Evidence is presented from measurements on ternary alloys that show that at least part of the extra-5f intensity is due to the hitherto missing main peak (or d-screened f-hole peak) just as in the 4f systems. The remaining intensity is consistent with a band structure DOS. (The compounds used were URh/sub 3/B/sub x/, UPd/sub x/Rh/sub 3-x/, ThBe/sub 13/, UIr/sub 3/, and UBe/sub 13/.) (DLC)
Date: December 1, 1986
Creator: Arko, A.J.; Yates, B.W.; Dunlap, B.D.; Koelling, D.D.; Mitchell, A.W.; Lam, D.J. et al.
Partner: UNT Libraries Government Documents Department

Electronic structure studies of YBa[sub 2]Cu[sub 3]O[sub x](6. 2 [le] x [le] 6. 9) using angle resolved photoemission

Description: Using high resolution angle resolved photoemission, the electronic structure of YBa[sub 2]Cu[sub 3]O[sub x] is examined when oxygen stoichiometries are varied in the range 6.2 [le] [times] [le] 6.9. Detailed measurements of the Fermi surface for YBa[sub 2]Cu[sub 3]O[sub 6.9] are presented and are compared with predictions of band theory. In the metallic region of the phase diagram, changes in the Fermi surfaces are measured as a function of oxygen stoichiometry. The electronic structure is monitored as the oxide changes from a metal to a semiconductor with additional oxygen depletion. For intermediate stoichiometries, effects of oxygen vacancy ordering are considered. Unusual resonant effects observed at several photon energies are examined as oxygen content is varied.
Date: November 1, 1992
Creator: Veal, B.W.; Liu, Rong; Paulikas, A.P.; Koelling, D.D.; Downey, J.W. (Argonne National Lab., IL (United States)); Shi, Hao (Argonne National Lab., IL (United States) Missouri Univ., Kansas City, MO (United States). Dept. of Physics) et al.
Partner: UNT Libraries Government Documents Department