Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session J13: Numerical Methods for Strongly Correlated Systems: Hubbard and QuasiParticle 
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Sponsoring Units: DCOMP Chair: James Davenport, Brookhaven National Laboratory Room: 309 
Tuesday, March 17, 2009 11:15AM  11:27AM 
J13.00001: Evaluation of timeresolved photoemission spectra from nonequilibrium, timedomain Green functions B. Moritz , T. P. Devereaux , H. R. Krishnamurthy , J. K. Freericks Recent experiments have shown the power of femtosecond timeresolved, pumpprobe photoelectron spectroscopy to probe, directly, the nonequilibrium, realtime dynamics of excitations in a correlated material. We use nonequilibrium dynamical meanfield theory to study the spinless FalicovKimball model driven (pumped) out of equilibrium by a constant electric field turned on at $t=0$. We demonstrate the proper evaluation of the timeresolved photoemission intensity as a function of pumpprobe delay for both metallic and Mottinsulating phases of the model and the dependence of the intensity profile on the specific details of the probe pulse's lineshape and duration. [Preview Abstract] 
Tuesday, March 17, 2009 11:27AM  11:39AM 
J13.00002: Mottlike behavior in the pseudogap region of the Hubbard model Dimitrios Galanakis , Karlis Mikelsons , Ehsan Khatami , Mark Jarrell , Alexandru Macridin , Michael Ma , Juana Moreno We study the phase diagram of the twodimensional Hubbard model using the Dynamical Cluster Approximation (DCA) in conjunction with the weakcoupling continuous time quantum Monte Carlo (CTQMC) as the cluster solver. We verify the existence of a quantum critical point at a finite electron doping which separates a fermi liquid region at low electron doping from the pseudogap region at high electron doping \footnote{Vidhyadhiraja et. al., arXiv:0809.1477v1}. In the pseudogap region the double occupancy, the two particle correlation functions and spectra reveal a synergism between the development of moment formation and the appearance of short ranged order. We discuss the connection between our results and experiments. [Preview Abstract] 
Tuesday, March 17, 2009 11:39AM  11:51AM 
J13.00003: Pairing instabilities and Bose condensation in Hubbard nanoclusters Gayanath Fernando , Kalum Palandage , Armen Kocharian , James Davenport Pairing instabilities found from exact studies of small Hubbard clusters with different topologies appear to provide answers to some long standing puzzles. Electronic charge and spin pairing instabilities in a phase space defined by temperature, magnetic field and chemical potential, lead to properties that are remarkably similar to correlated, inhomogeneous bulk systems such as the high temperature superconductors and colossal magnetoresistance materials. In particular, the role of square planar geometry is borne out when the vertex coupling in an octahedron is shown to have a detrimental effect on the negative charge and positive spin gaps, which are favorable to forming a Bose condensate in the region of instability. In addition, it is shown that magnetic flux can get trapped in stable minima at half integral units of the flux quantum. [Preview Abstract] 
Tuesday, March 17, 2009 11:51AM  12:03PM 
J13.00004: Functional renormalization group beyond the static approximation and its application to twodimensional Hubbard model. Hirokazu Takashima , Ryotaro Arita , Kazuhiko Kuroki , Hideo Aoki While the functional renormalization group(fRG) is a powerful theoretical method for strongly correlated electron systems which treats diagrams systematically within a framework of quantum field theory, the static approximation is adopted where the Matsubara frequency dependence of the fourpoint coupling and renormalization for the selfenergy are ignored. Here we propose a method to go beyond the static approximation by devising an efficient parameterization for the fourpoint coupling in the Matsubara frequency space, which is combined with a previous improved algorithm of ours[1] based on a Cartesian box discretization. [1] H. Takashima, R. Arita, K. Kuroki, and H. Aoki, to be published in J. Phys.: Conference Series,\textit{ LT25PROC484.} [Preview Abstract] 
Tuesday, March 17, 2009 12:03PM  12:15PM 
J13.00005: Parquet approximation calculation for the 2D Hubbard model Shuxiang Yang , Herbert Fotso , Jun Liu , Mark Jarrell , Eduardo D'Azevedo , Thomas Maier , Karen Tomko , Richard Scalettar , Thomas Pruschke We present a numerical solution of the parquet approximation on a halffilled 4x4 Hubbard cluster. The parquet formalism is a twoparticle self consistent set of equations relating the reducible, irreducible, and fully irreducible vertieces. The simplest approximation from this formalism is the socalled parquet approximation, in which the fully irreducible vertex is approximated by the bare interaction. Our results are compared with results from SelfConsistent 2ndorder approximation, Fluctuation Exchange (FLEX) approximation and the Determinental Quantum Monte Carlo (DQMC) calculation. [Preview Abstract] 
Tuesday, March 17, 2009 12:15PM  12:27PM 
J13.00006: Spatially inhomogeneous phase in the twodimensional repulsive Hubbard model ChiaChen Chang , Shiwei Zhang Using recent advances in the constrainedpath auxiliaryfield quantum Monte Carlo method, we study the ground state of the twodimensional, singleband Hubbard model at intermediate interactions ($2\le U/t \le 8$). In the first part of this study [1], we have determined the equation of state and also calculated the spinspin correlation functions in square lattices up to size $16\times 16$. Shell effects are eliminated and finitesize effects are greatly reduced by boundary condition integration. It was shown that, upon doping, the system separates into a region with antiferromagnetic (AF) order and a holecontaining region without AF order. In the second part, we study rectangular supercells up to $8\times 64$ to examine the nature of this inhomogeneous phase, in particular to probe phase separation versus stripes and spindensity waves of long wave lengths. [1] ChiaChen Chang and Shiwei Zhang, Phys. Rev. B 78, 165101 (2008) [Preview Abstract] 
Tuesday, March 17, 2009 12:27PM  12:39PM 
J13.00007: Inhomogeneous ground state in the Hubbard model: a meanfield study Jie Xu , ChiaChen Chang , Eric J. Walter , Shiwei Zhang We report unrestricted HartreeFock (UHF) results for the ground state of the singleband Hubbard model in two and threedimensions with repulsive onsite interaction and nearestneighbor hopping. At halffilling, the HartreeFock (HF) approach is sufficient to capture the basic physics of longrange antiferromagnetic order. Away from halffilling, many earlier HF calculations have been performed in the 2D Hubbard model, which indicated the formation of domain walls and stripes. We numerically solve the selfconsistent UHF equations for a range of densities at weak and intermediate interaction strengths. An annealing scheme coupled with multiple initial configurations is adopted to reach the global minimum. Our goal is to contrast the UHF ground state in the Hubbard model and the HF spindensity wave states in the continuum (jellium) [1]. A second goal is to obtain quantitative information of the UHF ground state for examination by accurate manybody methods such as quantum Monte Carlo. [1] A. W. Overhauser, Phys. Rev. 128, 1437 (1962); Shiwei Zhang and D.M.Ceperley, Phys. Rev. Lett. 100, 236404 (2008). [Preview Abstract] 
Tuesday, March 17, 2009 12:39PM  12:51PM 
J13.00008: Discontinuous quenching of quasiparticle states in nonequilibrium dynamical meanfield theory Ryan Heary , Jong Han In an effort to model strongly correlated heterojunctions in nonequilibrium we construct a nonequilibrium dynamical meanfield theory for the Hubbard model where each lattice site is a superposition of a leftmoving and rightmoving state. The left and right movers have the respective chemical potentials, $\mu_L=\frac{\Phi}{2}$ and $\mu_R=\frac{\Phi}{2}$, where $\Phi$ is the chemical potential bias. The quasi particle properties are calculated as a function of the Coulomb interaction, $U$, and $\Phi$. As the chemical potential bias is turned on we find that the quasiparticles become strongly renormalized. When $U_d [Preview Abstract] 
Tuesday, March 17, 2009 12:51PM  1:03PM 
J13.00009: Selfconsistent solution for the Hubbard model at the twoparticle and oneparticle level using the parquet formalism. Herbert Fotso , Shuxiang Yang , Jun Liu , Mark Jarrell , Eduardo D'Azevedo , Thomas Maier , Karen Tomko , Richard Scalettar The parquet Formalism is used to solve selfconsistently, both at the oneparticle and at the twoparticle levels, the Hubbard model on a 2D square lattice. The parquet equation and the BetheSalpeter equation are combined into one Newton fixed point problem which is then solved by taking advantage of the existing linear solvers such as GMRES and BiCGStab. Some quantities of interest are calculated and the results are compared to those of Determinental Quantum Monte Carlo (DQMC). We also discuss the importance of this work in the multiscale treatment of the High Tc Cuprates. [Preview Abstract] 
Tuesday, March 17, 2009 1:03PM  1:15PM 
J13.00010: Quantum Monte Carlo study of fewelectron concentric double quantum rings Leonardo Colletti , Francesc Malet , Marti Pi , Francesco Pederiva We consider fewelectron concentric double quantum rings with parabolic confining potential and compare the groundstate energies calculated by exact diagonalization of the Hamiltonian, accurate quantum Monte Carlo and local spindensity functional approaches. Electronic localization in one of the rings and the formation of rotating Wigner molecules is shown respectively from the onebody and the twobody density operators. As the confinement strength is finely increased, the circularlysymmetric electron density exhibits a radial crossover from the outer ring to the inner one without altering the angular character of the system. [Preview Abstract] 
Tuesday, March 17, 2009 1:15PM  1:27PM 
J13.00011: Accurate Determination of Tensor Network State of Quantum Lattice Models in Two Dimensions Tao Xiang , H.C. Jiang , Z.Y. Xie , Q.N. Chen , Z.Y. Weng We have proposed a novel numerical method to calculate accurately physical quantities of the ground state using the tensor network wave function in two dimensions. The tensor network wave function is determined by an iterative projection approach which uses the TrotterSuzuki decomposition formula of quantum operators and the singular value decomposition of matrix. The norm of the wave function and the expectation value of a physical observable are evaluated by a novel second renormalization group method of tensors. Our method allows a tensor network wave function with a high bond degree of freedom to be handled accurately and efficiently in the thermodynamic limit. For the Heisenberg model on a honeycomb or square lattice, our results for the ground state energy and the staggered magnetization agree well with those obtained by the quantum Monte Carlo and other approaches. [Preview Abstract] 

J13.00012: ABSTRACT WITHDRAWN 
Tuesday, March 17, 2009 1:39PM  1:51PM 
J13.00013: Electronic structure of La$M$O$_3$ (M=Ti$\sim$Cu) by GW approximation Yoshiro Nohara , Takeo Fujiwara We investigate the electronic structure of La$M$O$_3$ ($M=$Ti$\sim$Cu) by GW approximation. The calculated spectra show good agreement with the experimentally observed ones. The onsite Coulomb interaction are affected by strong screening mechanism in trivalent transition metal ion systems, which is qualitatively different from those in monooxides $M$O of divalent transition metals. In trivalent transition metal ion systems La$M$O$_3$, 3d electrons are affected by deep atomic potential. Therefore, the 3d orbital locates energetically much nearer to O 2p levels than in $M$O. Moreover, in the cases of $M^{3+}$=Cr$^{3+}$, Mn$^{3+}$ and Fe$^{3+}$ systems, transition metal ions are well spinpolarized, and 3d levels locate very near to O 2p levels. As a result, these systems have large screening effects due to the extended delectrons. In the cases of $M^{3+}$=Ni$^{3+}$ and Cu$^{3+}$, the systems are metallic and are affected by strong screening effects. In the other cases of $M^{3+}$= Ti$^{3+}$, V$^{3+}$, and Co$^{3+}$, there are small screening effects causing large static screened Coulomb interaction. [Preview Abstract] 
Tuesday, March 17, 2009 1:51PM  2:03PM 
J13.00014: GW correlation effects on the quasiparticle energies of Np and Pu Athanasios Chantis , Robert Albers , Axel Svane , Niels Christensen , Mark van Schilfgaarde , Takao Kotani We present results for the electronic structure of plutonium and neptunium by using a recently developed quasiparticle selfconsistent $GW$ method (QS$GW$). The selfconsistent $GW$ quasiparticle energies are compared to those obtained within the Local Density Approximation (LDA) for several volumes of the unit cell. The goal of the calculations is to understand systematic trends in the effects of electronic correlations on the quasiparticle energy bands as a function of the localization of the $f$ orbitals. We show that correlation effects narrow the $f$ bands in two significantly different ways. Besides the expected narrowing of individual $f$ bands (flatter dispersion), we find that an even more significant effect on the $f$ bands is a decrease in the crystalfield splitting of the different bands. We discuss how these changes affect the topology of the Fermi surface and we demonstrate the importance of the quasiparticle selfconsistency scheme in obtaining these results. [Preview Abstract] 
Tuesday, March 17, 2009 2:03PM  2:15PM 
J13.00015: Ground state properties of simple solids from GW calculations. Andrey Kutepov , Sergey Savrasov A novel selfconsistent implementation of Hedin's GW perturbation theory is presented. This finitetemperature implementation uses HartreeFock wave functions to represent Green's function. HartreeFock equations are solved with full potential linear augmented plane wave (FLAPW) method at each iteration of a selfconsistent cycle. With our approach we are able to calculate total energy and the ground state properties. As an example, the ground state properties of Na, Al, Si, and GaAs obtained with our new code are presented. [Preview Abstract] 
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