CMSN Coordination Meeting Agenda

 

(All talks will be held in 55 ROESSLER Lecture Hall located

in front of the Physics/Geology Building at UCD)

 

 

 

Saturday, September 15, 2007

 

 

8:00am
Breakfast, Lobby of 55 Roessler

 

 

MORNING SESSION 1 (Chair Warren Pickett)

 

8:50-9:00

Warren Pickett & Richard Scalettar (University of California, Davis)

Welcome

 

9:00-9:30

Jan Kunes (University of Augsburg)

Moment-Collapse Driven Mott Transition in MnO under Pressure

 

 

9:30-10:00

Alexandru Macridin (University of Cincinnati)

Hubbard model with phonons: Superconductivity, polaron formation and isotope effect.

 

10:00-10:30

Tom Devereaux (Stanford Synchrotron Radiation Laboratory)

Resonant and Non-Resonant Inelastic X-ray Scattering in Strongly Correlated Materials

 

 

10:30-11:00

Coffee Break + Discussions

 

 

MORNING SESSION 2 (Chair Mark Jarrell)

 

11:00-11:30

Takeshi Egami (University of Tennessee and Oak Ridge National Laboratory)

Dark Matter in the Cuprate Physics

 

11:30-12:00

Jim Tobin (Lawrence Livermore National Laboratory)

Proof of Dynamical Spin Shielding in Ce from Spin-Resolved Photoelectron Spectroscopy

 

12:00-12:30

Michael Manley (Lawrence Livermore National Laboratory)

Nonequilibrium creation of intrinsically localized vibrations

 

 

LUNCH

 

12:30-02:00

Lunch, Food set up in 432 Phy/Geo and utilize 430 Phy/Geo as well as 416 Phy/Geo.
Entree - Rainbow cheese tortellini

 

 

AFTERNOON SESSION 1 (Chair Andy McMahan)

 

02:00-02:30

Jian-Xin Zhu (Los Alamos National Laboratory)

Spectral Properties of delta-Plutonium: Sensitivity to 5f Occupancy

 

02:30-03:00

Henry Krakauer (College of William and Mary)

Finite-size corrections and other developments in auxiliary field quantum Monte Carlo

 

03:00-03:30

Steve White (University of California, Irvine)

DMRG study of the triangular lattice

 

 

03:30-04:00

Coffee Break + Discussions

 

 

AFTERNOON SESSION 2 (Chair Henry Krakauer)

 

04:00-04:30

Tony Gonis (Lawrence Livermore National Laboratory)

Self-interaction Free Local Approximation to Density Functional Theory and its Conventional Formulation

 

04:30-05:00

Wei Ku (Brookhaven National Laboratory)

Local excitations in strongly correlated multi-orbital systems:

effective kinetic effects in one- and two-particle channels

05:00-05:20
Magnus Lipp (Lawrence Livermore National Laboratory)

The Volume Collapse in Cerium Revisited

 

 

POSTER SESSION

 

05:30-06:30
Poster Session + Wine Reception

 

 

Dinner on your own

 

 

Sunday, September 16, 2007

 

 

8:30am
Breakfast, Lobby of 55 Roessler

 

 

MORNING SESSION 1 (Chair Adolfo Eguiluz)

 

9:00-9:30

Chris Marianetti (Lawrence Livermore National Laboratory)

The Fermi surface and heat capacity of Na0.3CoO2: A DMFT study

 

9:30-9:50

Simone Chiesa (University of California, Davis)

Spectral property of strongly correlated systems using grand-canonical averaging

 

9:50-10:10

Oscar Restrepo (Vanderbilt University)

Ab initio study of charge excitations in Na1/3CoO2 1.3H2O

 

10:10-10:30

Dmitri Volja (Brookhaven National Laboratory)

Charge Ordering  in Half-Doped Manganites: Weak Charge Disproportion and Leading Mechanisms

 

 

10:30-10:50

Coffee Break + Discussions

 

 

MORNING SESSION 2 (Chair Richard Scalettar)

 

10:50-11:10

Kevin Moore (Lawrence Livermore National Laboratory)

Rampant changes in 5f5/2 and 5f7/2 filling across the light and middle actinide metals: What this means for electronic-structure calculations

 

11:10-11:30

Scott McCall (Lawrence Livermore National Laboratory)

Evolving Magnetism from Self Damage in Pu and PuAm alloys

 

 

COORDINATION MEETING

 

11:30-12:30

Coordination Meeting

(those not affiliated with CMSN may safely skip)

 

Committee reports:

coordination: Savrasov,

code sharing: Pickett,

computing: Jarrell

CMSN topics discussions

 

 

LUNCH

 

12:30

Lunch, Food set up in 432 Phy/Geo and utilize 430 Phy/Geo as well as 416 Phy/Geo.
Santa Fe lunch buffet

 

 

ABSTRACTS

 

 

Simone Chiesa, University of California, Davis

 

Title: Spectral property of strongly correlated systems using grand-canonical averaging

 

Abstract: I will review the idea behind grand-canonical averaging applied to exact diagonalization calculations at zero temperature. Results for the spectral function for the clean and disordered Hubbard model are presented. I will also comment on the possibility of using the grand-canonical wave function as an ansatz for more refined calculations.

 

 

Tom Devereaux, Stanford Synchrotron Radiation Laboratory

 

Title: Resonant and Non-Resonant Inelastic X-ray Scattering in Strongly Correlated Materials

 

Abstract: With recent developments in third generation light sources and detectors, and wealth of information pertaining to charge dynamics has emerged in the cuprates. In this talk I will DMFT-based calculations for non-resonant inelastic x-ray scattering in model systems, and present cluster calculations for resonant inelastic x-ray scattering in edge-shared copper oxide systems, such as Li2CuO2 and CuGeO3, appropriate for hard x-ray scattering such as the copper K-edge. The energies, orbital character and resonance profiles of excitations which can be probed via RIXS will be discussed and compared with experiments.

 

 

Takeshi Egami, University of Tennessee and Oak Ridge National Laboratory

 

Title: Dark Matter in the Cuprate Physics

 

Abstract: Many theories of high-temperature superconductivity assume the presence of short-range antiferromagnetic (AFM) correlation in the cuprates, and the neutron inelastic scattering data certainly suggest such a presence.  But nobody has measured it directly; only indirect evidences exist.  Furthermore the total spectral weight of the measured neutron scattering intensity is far below what is expected from the sum-rule.  The rest of the spectral weight may be called the dark matter in the cuprate physics.  Our recent neutron scattering measurement on YBCO6.6 suggests that a large part of the intensity condensates into the spin-glass-like state below the pseudo-gap temperature.  While the conventional theories, including the t-J model, assume that the predominant magnetic interaction is the AFM exchange, our results suggest some of the magnetic interactions are ferromagnetic, presumably due to the holes localized on oxygen.  These results challenge the conventional view on the magnetism in the cuprates and their role in high-temperature superconductivity.

 

 

Tony Gonis, Lawrence Livermore National Laboratory

 

Title: Self-interaction Free Local Approximation to Density Functional Theory and its Conventional Formulation

 

Abstract: We propose a new functional form for the implementation of the local-density approximation to density functional theory that is free of self-interaction effects. The functional is obtained through the replacement of the classical (Hartree) expression for the Coulomb energy with the quantum-mechanical one in terms of the two-partricle correlation function constructed out of the single-particle orbitals obtained through the local approximation. It is shown that the new functional leads to ground-state energies that form an upper bound to the exact ground-state energies of a system in agreement with formal results and an expression for the exchange-correlation potential is provided. A comparison with the properties of the conventional formulation of the LDA is given along with a motivation for proposing the present formalism.

 

 

Wirawan Purwanto, Hendra Kwee, Henry Krakauer, and Shiwei Zhang

College of William & Mary

 

Title: Finite-size corrections and other developments in auxiliary field quantum Monte Carlo

 

Abstract: An a posteriori method is presented that delivers rapidly convergent finite-size corrections of many-body electronic structure calculations, accelerating the convergence of costly supercell calculations. The method improves upon traditional one-body corrections from mean-field methods such as density functional theory, by including two-body terms obtained from a homogeneous electron gas in finite volume. These corrections are post processing corrections that can be applied to any previously obtained many-body results without having to repeat expensive calculations. Applications of the method to the P2 molecule, bulk semiconducting Si, and metallic Na show improved error correction. Generalizations to other density functionals and to spin-polarized systems should be straightforward. Time permitting, new developments in the phaseless auxiliary field quantum Monte Carlo method [1-7] will be reported on bond-breaking and excited states in difficult molecular systems.

 

References

 

[1] S. Zhang and H. Krakauer. Quantum Monte Carlo method using phase-free random walks with Slater determinants. Phys. Rev. Lett., 90(13):136401, Apr 2003.

[2] W. A. Al-Saidi, H. Krakauer, and S. Zhang. Auxiliary-field quantum Monte Carlo study of TiO and MnO molecules. Phys. Rev. B, 73:075103, 2006.

 

[3] W. A. Al-Saidi, S. Zhang, and H. Krakauer. Auxiliary-field quantum Monte Carlo calculations of molecular systems with a gaussian basis. J. Chem. Phys., 124:224101, 2006.

 

[4] W. A. Al-Saidi, H. Krakauer, and S. Zhang. Auxiliary-field quantum Monte Carlo study of first- and second-row post-d elements. J. Chem. Phys., 125:154110, 2006.

 

[5] W. A. Al-Saidi, H. Krakauer, and S. Zhang. A study of H + H2 and several H-bonded molecules by phaseless auxiliary-field quantum Monte Carlo with plane wave and gaussian basis sets. The Journal of Chemical Physics, 126(19):194105, 2007.

 

[6] M. Suewattana, W. Purwanto, S. Zhang, H. Krakauer, and E. J. Walter. Phaseless auxiliary-field quantum Monte Carlo calculations with plane waves and pseudopotentials: Applications to atoms and molecules. Physical Review B (Condensed Matter and Materials Physics), 75(24):245123, 2007.

 

[7] W. A. Saidi, S. Zhang, and H. Krakauer. Bond breaking with auxiliary-field quantum Monte Carlo. J. Chem. Phys., 2007. in press.

 

 

Wei Ku, Brookhaven National Laboratory

 

Title: Local excitations in strongly correlated multi-orbital systems:

effective kinetic effects in one- and two-particle channels

 

Abstract: Resent progress in theoretical development for the study of local quasi-particle and particle-hole excitations in strongly correlated multi-orbital systems will be reported.  The developed theoretical framework is based on first-principles derived effective interacting Hamiltonian and the Wannier orbitals, and is designed to investigate beyond-mean-field quantum fluctuation in real space.  The strong "local" interaction will be treated exactly, leaving the non-local kinetic effects as "perturbation" to the local multiplets.  A practical approximation will be discussed to include the effective kinetic terms in both one- and two-particle channels that approach the exact results in both strong and weak coupling limit.

 

 

Jan Kunes, University of Augsburg

 

Title: Moment-Collapse Driven Mott Transition in MnO under Pressure

 

Abstract: The metal-insulator transition in correlated electron systems, where electron states transform from itinerant to localized, has been one of the central themes of condensed matter physics for more than half a century.  The persistence of this question has been a consequence both of the intricacy of the fundamental issues and the growing recognition of the complexities that arise in real materials, even when strong repulsive interactions play the primary role. The initial concept of Mott was based on the relative importance of kinetic hopping (measured by the bandwidth) and on-site repulsion of electrons. Real materials, however, have many additional degrees of freedom that, as is recently attracting note, give rise to a rich variety of scenarios for a ``Mott transition.''

Here we show that the computational theory of strongly correlated systems has progressed to the point where the Mott transition of the classic correlated insulator MnO can be obtained directly from first principles, and the mechanism identified as collapse of the magnetic moment due to increase of the crystal field splitting, rather than to variation of the bandwidth.

 

 

Magnus Lipp, Lawrence Livermore National Laboratory

 

Title: The Volume Collapse (VC) in Cerium Revisited

 

Abstract: Despite extensive experimental and theoretical efforts, much of the available information about the phase diagram of cerium and its large VC appears incomplete or controversial.  Results are easily affected by sample treatment and impurities or have been obtained several decades ago. Moreover, much of the previous work was performed at room temperature or lower. Only a few investigations exist at higher temperature near the critical point of the VC. However, precise knowledge of the equation of state (EOS) especially at temperatures higher than the critical point would benefit modern theoretical considerations expecting the cause of the VC to be of purely electronic origin. In that case some remnant of the VC might persist as a softness of the EOS, possibly extending into the liquid phase.

 

 

Alexandru Macridin, University of Cincinnati

 

Title: Hubbard model with phonons: Superconductivity, polaron formation and isotope effect.

 

Abstract: A large body of experimental evidence shows strong interaction between electrons and lattice vibrations in high Tc superconductors. Motivated by this we investigate the effect of dynamical Holstein, buckling and breathing phonons on the physics of the 2D Hubbard model at small doping using a cluster meanfield approximation. The interplay of the antiferromagnetic correlations present in the system and the electron phonon coupling results in a synergistic

enhancement of both polaron formation and antiferromagnetism. We find that phonons cause an apparent enhancement of the effective pairing interaction but in spite of that the strong renormalization of the charge carriers mobility associated with polaron formation leads to a suppression of superconductivity in the region of parameter space relevant for cuprate superconductors.

 

Michael Manley, Lawrence Livermore National Laboratory


Title: Nonequilibrium creation of intrinsically localized vibrations

Abstract: In the presence of non-linear forces the frequencies of vibrating atoms depends on amplitude, allowing a local amplitude fluctuation to develop a frequency that does not match its surroundings. In this situation the vibration may not resonate with other modes causing energy to become trapped in an intrinsically localized mode (ILM) - also called 'discrete breather' or 'lattice soliton'. Evidence of this effect in a conventional solid was first discovered a year ago in the form of a new mode forming in uranium at high temperatures. To make the case that this mode was the elusive ILM, however, required a complex process of elimination, where defect modes and other structural effects were ruled out. Recently, we developed a more direct approach where ILMs are actively created at low temperatures using high-energy inelastic x-ray and neutron scattering. The ILM creation excitation has the same structure as the ILM vibration but occurs at energies ten times higher than conventional lattice excitations, cleanly separating it from modes associated with crystal imperfections. The discovery of this excitation not only proves the existence of ILMs in uranium but also points to a new path for finding ILMs in other materials. If time permits I might also discuss some preliminary work on the creation of ILMs in ionic crystals.

 

 

Chris Marianetti, Lawrence Livermore National Laboratory

 

Title: The Fermi surface and heat capacity of Na0.3CoO2: A DMFT study

 

Abstract: We use density functional theory (DFT) and the dynamical mean-field theory (DMFT) to calculate the Fermi surface and heat capacity for Na0.3CoO2.  We resolve the conflicting outcomes of previous calculations by demonstrating that the nature of the calculated Fermi surface depends sensitively upon the bare Hamiltonian, and in particular the crystal field splitting.  By calculating both the Fermi surface and the heat capacity, we show that the only consistent conclusion is that the eg pockets are not present at the Fermi surface.

 

 

S.K. McCall1, M.J. Fluss1, B.W. Chung1, and R.G. Haire2

1 Lawrence Livermore National Laboratory

2Oak Ridge National Laboratory

 

Title: Evolving Magnetism from Self Damage in Pu and PuAm alloys

 

Abstract: As a consequence of the unusual nature of Pu's electronic structure it is remarkably sensitive to perturbations, especially disorder.  This talk will focus on the changes in the magnetic properties that arise in Pu alloys from the introduction of disorder.  One method of introducing disorder in Pu is to exploit the natural radioactive processes through an a-decay plus U-recoil create damage cascades of vacancies and interstitials.  These defects are observable as an increase in the low temperature magnetization, which can be removed by thermal annealing above room temperature and corresponding return of the magnetization to its initial value.  Thus the radioactive decay provides a reversible method for adding disorder to the system.  A second method to increase disorder in Pu alloys is to dope the system with Am, which maintains the delta phase Pu structure to high Am concentrations (~80% Am), while simultaneously expanding the lattice, thus acting as negative pressure on the Pu as well as adding disorder to the system.  The influence on the magnetic properties of these two forms of disorder will be discussed.  Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48

 

 

K.T. Moore1*, G. van der Laan2, M.A. Wall1, A.J. Schwartz1, R.G. Haire3

1Lawrence Livermore National Laboratory, Livermore, California 94550, USA.

2Magnetic Spectroscopy Group, Daresbury Laboratory, Warrington WA4 4AD, UK.

3Oak Ridge National Laboratory, MS-6375, Oak Ridge, Tennessee 37831, USA.

 

Title: Rampant changes in 5f5/2 and 5f7/2 filling across the light and middle actinide metals: What this means for electronic-structure calculations

 

Abstract: We examine the branching ratio of the N4,5 (4d ® 5f ) spectra of Th, U, Np, Pu, Am, and Cm metal using electron energy-loss spectroscopy (EELS) in a transmission electron microscope (TEM), together with many-electron atomic spectral calculations and the spin-orbit sum rule. Our results show that: 1) The actinide metals Pu, Am, and Cm exhibit intermediate coupling. 2) The intermediate coupling values for the 5f states as calculated using a many-electron atomic model are correct for the actinides, this being proven by our new results for curium. 3) The EELS branching ratio is sensitive to the degree of 5f electron delocalization, which is illustrated by the transition from LS to intermediate coupling between U and Pu. 4) Plutonium metal, which is arguably the most difficult actinide to deal with, has a 5f 5 electron configuration with the 5f states operating in intermediate coupling that is very near the jj limit.

 

 

Oscar Restrepo, Vanderbilt University

 

Title: Ab Initio evaluation of charge excitations in Na1/3CoO2 yH2O within

time-dependent density functional theory

 

Abstract: We present ab initio results for the spectrum of charge excitations in Na1/3CoO2 yH2O and Na1/3CoO2.  Our results are discussed in the light of recent electron-loss-spectroscopy (EELS) and resonant inelastic x-rays scattering (RIXS) investigations.  The measured spectra feature a sharp loss at about 10eV which has been interpreted in terms of a conventional plasmon picture.  We show that the loss corresponds to a collective mode involving d-d on-site charge fluctuations coupled via quadrupolar interactions.  The absence of conventional Landau damping is a consequence of this interpretation.  The role of microscopic charge fluctuations  (crystal local fields) on the short-length scale dictated by the strongly-inhomogeneous electronic environment in this layered compound is highlighted — it determines the overall lineshape of the spectrum.  We also discuss lower-energy excitations of single-particle nature.  It is argued that ab initio theory is essential to disentangle the physics of the excitations in complex compounds.  The role of supercomputing environments such as the Bassi machine at NERS is highlighted.  For Na1/3CoO2 yH2O we deal with 44 atoms in the primitive unit cell, and must invert dielectric matrices (with the ensuing evaluations of an enormous number of matrix elements) of rank at least 150.  Calculations for larger systems involving strongly-correlated materials will require algorithmic improvements, and access to even more powerful architectures.

 

 

Jim Tobin, Lawrence Livermore National Laboratory

 

Title: Proof of Dynamical Spin Shielding in Ce from Spin-Resolved Photoelectron Spectroscopy

 

Abstract: Using Fano Effect measurements upon polycrystalline Ce, we have observed a phase reversal between the spectral structure at the Fermi Edge and the other 4f derived feature near a binding energy of 2 eV. The Fano Effect is the observation of spin polarized photoelectron emission from NONMAGNETIC materials, under chirally selective excitation, such as circularly polarized photons. The observation of phase reversal between the two peaks is a direct experimental proof of Kondo shielding in Ce, confirming the predictions of Gunnarsson and Shoenhammer, albeit with a small modification.

 

 

Dmitri Volja1,2, Wei-Guo Yin1, Wei Ku1

1 Brookhaven National Laboratory
2 State University of New York, Stony Brook

Title: Charge Ordering  in Half-Doped Manganites: Weak Charge Disproportion and Leading Mechanisms

 

Abstract: The current puzzle of weak charge disproportion experimentally observed in half-doped manganites which has long been interpreted in the picture of strong Mn3+/Mn4+ charge/orbital order is resolved by a novel Wannier states analysis of the LDA+U electronic structure. Strong electron itinerancy in this charge-transfer system significantly delocalizes the occupied low-energy ``Mn3+ states such that charge leaks into the Mn4+ -sites. Based on a realistic effective Hamiltonian derived from first-principles calculations, we further quantify the leading mechanisms of the charge-orbital orders and find that both electron-lattice and electron-electron interactions are important.

 

 

Steve White, University of California, Irvine

 

Title: DMRG study of the triangular lattice

 

Abstract: The density matrix renormalization group (DMRG) is primarily a 1D simulation method for quantum lattice systems which can also study 2D strips and ladders. Two recent advances greatly improve our ability to study ordering in 2D systems. I will discuss the application of these ideas to the triangular lattice Heisenberg model.

 

 

Jian-Xin Zhu, Los Alamos National Laboratory

 

Title: Spectral Properties of delta-Plutonium: Sensitivity to 5f Occupancy

 

Abstract: By combining the local density approximation (LDA) with dynamical mean field theory (DMFT), we report a systematic analysis of the spectral properties of delta-plutonium with varying 5f occupancy. The LDA Hamiltonian is extracted from a tight-binding (TB) fit to full-potential linearized augmented plane-wave (FP-LAPW) calculations. The DMFT equations are solved by the exact quantum Monte Carlo (QMC) method and the Hubbard-I approximation. We have shown for the first time the strong sensitivity of the spectral properties to the 5f occupancy, which suggests using this occupancy as a fitting parameter in addition to the Hubbard U. By comparing with PES data, we conclude that the open shell 5f5 configuration gives the best agreement, resolving the controversy over 5f open shell versus close shell atomic configurations in delta-Pu.

 

 

 

POSTERS

 

 

 

Tom Berlijn, Weiguo Yin, and Wei Ku

Title: Symmetry Respecting Wannier Functions: Gapless Charge Density Waves in 2H TaSe2

 

 

Cheng-Lin Yeh, and Wei Ku

Title: Real-Space Effective Two-Particle Kinetic Approach for Linear Response in Strongly Interacting Systems

 

 

Chi-Cheng Lee, Wei Ku, and B. C. Larson

Title: Electronic Symmetry Breaking Probed via Local In-Gap Excitations in NiO and CoO: Application of First-Principles Wannier Functions to Linear Response of Strongly Correlated Systems

 

 

K.-W. Lee, J. Kunes, R. T. Scalettar, and W. E. Pickett

Title: Correlation Effects in the Triangular Lattice Single-band System LixNbO2

 

 

Wirawan Purwanto, Henry Krakauer, Shiwei Zhang, and Wissam Al-Saidi

Recent advances in auxiliary-field quantum Monte Carlo: Applications to F2 and C2 potential energy surfaces

 

 

Erik Ylvisaker, A. K. McMahan, R. T. Scalettar and W. E. Pickett

DMFT Study of the Valence Transition in Yb.

 

 

Zhiping Yin and W. E. Pickett

Stability of the Gd Magnetic Moment to the 500 GPa Regime .

 

 

D. Kasinathan, K. Koepernik, and W. E. Pickett

Pressure-Driven Magnetic Moment Collapse in the Ground State of MnO.