Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session D13: Computational Methods: Strongly Correlated and Many Body Systems |
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Sponsoring Units: DCOMP Chair: Mark Jarrell, University of Cincinnatti Room: Morial Convention Center 204 |
Monday, March 10, 2008 2:30PM - 2:42PM |
D13.00001: Maximally-localized Wannier functions for GW quasiparticles D.R. Hamann, David Vanderbilt Recent efforts carrying the GW many-body approximation to self-consistency have given improved electronic-structure results.$^{1}$ However, one is left with self-energy operators only on the grid of \textbf{k} points used for Brillouin-zone integration, unlike the case of DFT where the local self-consistent potential allows calculation of the band structure on arbitrary \textbf{k} points (e.g., along symmetry lines). As maximally-localized Wannier functions$^{2}$ (MLWF) provide a basis for a highly accurate approach to band interpolation, we have combined the \textsc{wannier90} code for MLWF with the self-consistent GW capabilities of the \textsc{abinit} code to efficiently extend the GW grid calculation to a full band structure. MLWF also provide an intuitive picture of the orbital character and bonding of groups of bands, as well as a quantitatively accurate measure of electric polarization.$^{2}$ Differences between quasiparticle$^{3}$ MLWF and their LDA counterparts examined to date (Si and perovskite SrZrS$_{3}$) have proven small, but the visualization of significant many-body effects through MLWF remains an intriguing possibility. 1. F. Bruneval \textit{et al}., Phys. Rev. B \textbf{74}, 045102 (2006). 2. N. Marzari and D. Vanderbilt, Phys. Rev. B \textbf{56}, 12 847 (1997). 3. M. van Schilfgaarde \textit{et al}., Phys. Rev. Lett. \textbf{96}, 226402 (2006). [Preview Abstract] |
Monday, March 10, 2008 2:42PM - 2:54PM |
D13.00002: Ab initio calculation of the excited state properties of spiropyran Emmanouil Kioupakis, Steven G. Louie The photochromism of spiropyran/merocyanine molecules has been the subject of many experimental and theoretical studies. However, several questions remain open, in particular the excited state dynamics and the role of the triplet state. In this work, we use ab initio techniques based on Density Functional Theory and Green's functions methods based on the GW approximation to the electron self energy and Bethe-Salpeter equations to study the ground and excited states of spiropyran/merocyanine for various geometries. Our results are compared with previous work. This work was supported by National Science Foundation Grant No. DMR07-05941, the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Computational resources have been provided by NERSC and TeraGrid resources provided by SDSC and Indiana University. [Preview Abstract] |
Monday, March 10, 2008 2:54PM - 3:06PM |
D13.00003: All-electron GW calculation of vanadium dioxide Rei Sakuma, Takashi Miyake, Ferdi Aryasetiawan We present the results of the GW calculation of metallic and insulating vanadium dioxide using a full-potential LMTO basis set. Our calculations show that it is crucial to take into account both the frequency dependence and the off-diagonal elements of the self-energy. We find that the usual 1-shot GW scheme, where the frequency expansion of the self-energy is truncated in the first-order, yields a large error ($>0.1$eV) in quasiparticle energies due to the unsmoothness of the self- energy. In both phases, the dynamical correlation effect within RPA leads to a plasmon satellite above the Fermi level, but not below. This difference can be attributed to matrix element effects. Our 1-shot GW calculation does not reproduce insulating VO$_{2}$ due to the mixing of conduction and valence bands in the LDA calculation, and we reconstruct G and W by updating the quasiparticle wavefunctions and energies to obtain the band gap. The result indicates the importance of self-consistency in GW calculations. Our results are more in line with the Peierls picture of gap opening due to the lattice distortion, rather than the Motto-Hubbard picture of strong correlations. [Preview Abstract] |
Monday, March 10, 2008 3:06PM - 3:18PM |
D13.00004: GW-based \textit{ab initio} downfolding aiming at strongly correlated electron system Kazuma Nakamura, Taichi Kosugi, Yoshihide Yoshimoto, Ryotaro Arita, Masatoshi Imada Aiming at \textit{ab initio} description of real complex systems under effects of strong electron correlations, we develop a GW-based downfolding scheme formulated in the plane-wave basis set. Our method is successfully applied to organic conductors, the family of (BEDT-TTF)$_{2}$X. At the heart of our downfolding scheme lies utilizing the energy hierarchy of the system [1]: The low-energy hierarchy near the Fermi level (\textit{$\varepsilon $}$_{ f}\pm $2$\sim $3 eV) determines physics while is affected by the remaining high-energy part of hierarchy. We renormalize the high-energy part into low energy, based on the GW scheme. The renormalization generates a low-energy model characterized by renormalized transfers and effective screened Coulomb/exchange interactions, having frequency dependence arising from retarded screening by eliminated high-energy electrons. Thus, the low-energy frequency-dependent effective model is mapped out from the whole high- plus low-energy system in an \textit{ab initio} procedure. [1] F. Aryasetiawan \textit{et al}., Phys. Rev. B \textbf{70}, 19514 (2004); I. V. Solovyev and M. Imada, \textit{ibid}. \textbf{71}, 045103 (2005). [Preview Abstract] |
Monday, March 10, 2008 3:18PM - 3:30PM |
D13.00005: GW Study of Actinides: $\alpha$-Uranium and $\delta$-Plutonium R.C. Albers, A.N. Chantis, M. van Schilfgaarde, T. Kotani We have applied the recently developed Quasiparticle Self-Consistent GW (QSGW) method to $\alpha$-U and $\delta$-Pu. This is the first time that the f-orbital electron-electron interactions in actinides have been treated by a first-principles method that goes beyond the level of the generalized gradient approximation. We show that the QSGW approximation for U predicts a significant f-band narrowing when compared to GGA band-structure results. However, because of the low f-electron occupation number in U, ground-state properties are not significantly affected. This provides the first formal justification for the success of the LDA and GGA calculations in describing the gound-state properties of this material. For Pu we find that QSGW, like conventional band-structure calculations, predicts a static magnetic ground-state in contradiction with experiment. A non-magnetic solution is also presented. For $\delta$-Pu we show that the QSGW approximation predicts even stronger band narrowing than for U. Because of this and a larger f-occupation, the ground state properties are affected much more significantly than for U. Overall, because of its better treatment of correlation, we suggest that the QSGW solution rather than GGA should be a better starting point for future Dynamical Mean Field Theory (DMFT) and other correlation methods. [Preview Abstract] |
Monday, March 10, 2008 3:30PM - 3:42PM |
D13.00006: The formation of stripes and the pairing of charge carriers in anisotropic materials K.J.E. Vos, C. Povey, J.M. Tipper We have examined the formation of stripes and pairing in the anisotropic t - J model. We have used exact diagonalization methods on several different cluster sizes to examine the underdoped region. Evidence of unidirectional stripe formation in the charge and spin correlations was found. We have determined that the formation of stripes parallel to the Cu-O-Cu bonds enhances pairing and in the bulk limit there is a finite range of doping concentration where hole pairs will form. As the material becomes more anisotropic there is a phase transition that destroys the stripe. These results are consistent with the experimental data. [Preview Abstract] |
Monday, March 10, 2008 3:42PM - 3:54PM |
D13.00007: Theory of the Normal State of the Copper-Oxide Superconductors Ting Pong Choy, Robert G. Leigh, Philip Phillips We show here that many of the normal state properties of the cuprates are consequences of the new charge 2e boson which we have recently (Phys. Rev. Lett. {\bf 99}, 46404 (2007) and arXiv:0707.1554) shown to exist in the exact low-energy theory of a doped Mott insulator. In particular, the 1) mid-infrared band, 2) the $T^2$ contribution to the thermal conductiivty, 3) the pseudogap, 4) the bifurcation of the electron spectrum below the chemical potential as recently seen in angle-resolved photoemission, 5) insulating behaviour away from half-filling, 6) the high and low-energy kinks in the electron dispersion and 7) T-linear conductivity all derive from the charge 2e boson. We also calculate the inverse dielectric function and show that it possesses two dispersing particle-hole branches as a function of momentum in the lightly doped regime. The second of the two branches is mediated by a new charge e composite excitation formed from the charge 2e boson and represents a distinctly new prediction of this theory. We propose that electron energy loss spectroscopy at finite momentum and frequency can be used to probe the existence of the second particle-hole branch. [Preview Abstract] |
Monday, March 10, 2008 3:54PM - 4:06PM |
D13.00008: Imaginary-time formulation for strongly correlated transport in steady-state nonequilibrium Jong E. Han, Ryan J. Heary We formulate steady-state nonequilibrium from the scattering state theory and show that an imaginary-time formalism exists for strongly correlated transport calculations in quantum dot devices\footnote{J. E. Han, R. J. Heary, Imaginary-time formulation of steady-state nonequilibrium: application to strongly correlated transport {\it accepted to Phys. Rev. Lett.} arXiv:0704.3198v2.}. Equilibrium imaginary-time method is extended to the steady-state nonequilibrium by mapping the chemical potential difference in the quantum got device into complex Matsubara voltage. Due to this formal similarity between equilibrium/nonequilibrium theories, we readily apply an equilibrium numerical technique to calculate the strong correlation effects in nonequilibrium. We use quantum Monte Carlo method to calculate Green functions at each Matsubara voltage and, after a numerical analytic continuation, we obtain nonperturbative Green function far from equilibrium. We show numerical results for the evolution of Kondo anomaly as a function of finite bias. We also discuss the splitting of Kondo anomaly at finite magnetic fields. [Preview Abstract] |
Monday, March 10, 2008 4:06PM - 4:18PM |
D13.00009: Electron fractionalization and statistics of holons in doped quantum dimer models Didier Poilblanc I introduce a doped two-dimensional quantum dimer model describing a doped Mott insulator and retaining the original Fermi statistics [1]. This model shows a rich phase diagram including a d-wave hole-pair superconductor breaking translation symmetry (supersolid) at small doping, a bosonic superfluid at large doping and an exotic intermediate phase in-between. The hole kinetic energy is shown to favor binding of topological defects to the fermionic holons turning them into bosons, in agreement with arguments based on RVB wave-functions. Results are discussed in the context of cuprates superconductors and compared with those of a related bosonic doped quantum dimer model [2]. [1] D. Poilblanc, arXiv:0711.2229. [2] A. Ralko, F. Mila, and D. Poilblanc, Phys. Rev. Lett. 99, 127202 (2007). [Preview Abstract] |
Monday, March 10, 2008 4:18PM - 4:30PM |
D13.00010: Improvement on the STLS Approach and its Application to the Spin Fully-Polarized Low-Density Electron Gas Yasutami Takada, Kanako Yoshizawa Four decades ago, Singwi, Tosi, Land, and Sj\"olander (STLS) proposed a theory that treats the local-field factor $G(q)$ and the static structure factor $S(q)$ in a self-consistent fashion. Because of its simplicity in practical calculations and reasonably good results for the correlation energy, this STLS framework has been recognized as a powerful theoretical tool to study short-range correlation beyond the RPA. At the same time, however, it has been realized that the STLS scheme has several shortcomings; among others, it does not satisfy the Pauli principle as exemplified by the fact that the on-top parallel-spin pair distribution function $g_{\uparrow\uparrow} (0)$ becomes negative. In view of this situation, we propose an improved STLS approach in which a special procedure is added to the original STLS framework in order to impose the Pauli principle. This new scheme is successfully applied to the spin-fully polarized electron gas with the electron density parameter $r_s$ ranging from 1 to 100 to find that the correlation energy obtained by quantum Monte Carlo simulations is reproduced very accurately, along with satisfying $g_{\uparrow\uparrow}(0) = 0$ and the non- negativity condition $g_{\uparrow\uparrow}(r) \geq 0$. Implications of our results will be given in the context of the contribution to the density functional theory as well as to the spin structure of the Wigner-lattice state. [Preview Abstract] |
Monday, March 10, 2008 4:30PM - 4:42PM |
D13.00011: Role of phonons and of finite temperature on the spectral function of a single hole in a quantum antiferromagnet Satyaki Kar, Efstratios Manousakis Thermal broadening as well as the role of optical phonons are studied for a single-hole in a quantum antiferromagnet within the t-J (and the t-t'-t"-J) model. The non-crossing approximation (NCA) as well as the effect of vertex corrections (up to second order) are used to describe the coupling to spin waves and phonons up to intermediate range of coupling. Phonons at finite temperature are seen to broaden the quasiparticle peak and the string excitations are found to survive up to an intermediate phonon-coupling regime beyond which the NCA is expected to break down. The qualitative features of our results compare reasonable well with the recent high resolution angular resolved photoelectron spectroscopy. [Preview Abstract] |
Monday, March 10, 2008 4:42PM - 4:54PM |
D13.00012: The Green's Function of the 1D Breathing-Mode Polaron Glen Goodvin, Mona Berciu We apply the Momentum Average approximations MA(0) and MA(1) to study the properties of the one-dimensional breathing-mode polaron. The results are analytical, numerically trivial to evaluate, exact for both zero bandwidth and for zero electron-phonon coupling, and are accurate everywhere in parameter space. Comparison with recent numerical data confirms this accuracy. We also show that by applying MA as a variational method with a suitably chosen enlarged subspace, we can obtain extremely high accuracy for both ground state and higher energy state properties. With only a slight increase in computational effort this allows us to obtain ground state and momentum-dependent results well within 0.1\% error of the exact numerical data currently available. Although this work specifically looks at the breathing-mode model, we demonstrate that MA is applicable to all momentum dependent electron-phonon coupling models, and its accuracy can always be improved by systematically improving the approximation itself or by working in an enlarged variational subspace. [Preview Abstract] |
Monday, March 10, 2008 4:54PM - 5:06PM |
D13.00013: Competition between pseudogap phase and d-wave superconductivity in the limit of large number of coupled 1D chains Enrico Perfetto, Jose Gonzalez We study the electronic instabilities in a quasi-one-dimensional Hubbard model formed by a large array of Hubbard chains. We go beyond the renormalization group solution of the model, by incorporating the nonperturbative bosonization method for the analysis of the quasiparticle properties. We show that when the Fermi level is at the Van Hove singularity the anomalous electron dimension diverges at the Fermi points closer to the saddle points of the 2D dispersion. Such divergence competes with the d-wave superconducting instability, but the suppression of the quasiparticle weight around the hot spots at (pi,0) and (0,pi) takes place first. This behaviour survives when the number of coupled chains becomes large, suggesting that the development of the pseudogap should survive in the 2D limit. [Preview Abstract] |
Monday, March 10, 2008 5:06PM - 5:18PM |
D13.00014: Extensions of the Momentum Average approximation Mona Berciu, Lucian Covaci We consider a well studied problem, the formation of polarons. Even for the simplest electron-phonon interaction (the Holstein model), an exact solution is only known in the asymptotic limits of zero coupling or zero free-electron bandwidth. A simple analytical approximation that turns out to be accurate for all coupling strengths (the Momentum Average approximation) has only been found recently. We discuss the extension of this method to various other situations in which polaron physics might be important. We show how the Momentum Average approximation can be used in answering questions regarding coupling of electrons to multiple phonon branches, formation of polarons in the presence of magnetic fields and the existence of multiple electron bands. [Preview Abstract] |
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