Outline Collaborators References Introduction to extensions of DMFT
Outline, Collaborators, References Introduction to extensions of DMFT for applications to electronic structure. [ S. Savrasov and GK condmatt 0308053] § C-DMFTstudy of the Mott transition. [O. Parcollet G. Biroli and GK cond-mat 0308577 ] n Applications to materials: MIT in Ti 2 O 3[S. Poteryaev S. Lichtenstein and GK cond-mat 0311319 ] n Delta –Epsilon transition in Plutonium [Xi Dai S. Savrasov GK A Migliori H. Ledbetter E. Abrahams Science 300, 953 (2003)] n Outlook. n THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Dynamical Mean Field Theory (DMFT) Cavity Construction: A. Georges and G. Kotliar PRB 45, 6479 (1992). THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
DMFT Cavity Construction. A. Georges and G. Kotliar PRB 45, 6479 (1992). First happy marriage of atomic and band physics. Reviews: A. Georges G. Kotliar W. Krauth and M. Rozenberg RMP 68 , 13, 1996 Gabriel Kotliar and Dieter Vollhardt Physics Today 57, (2004) THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
EDMFT [H. Kajueter Rutgers Ph. D Thesis 1995 Si and THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Site Cellular DMFT. C-DMFT. G. Kotliar, S. . Savrasov, G. Palsson and G. Biroli, Phys. Rev. Lett. 87, 186401 (2001) tˆ(K) hopping expressed in the superlattice notations. • Other cluster extensions (DCA Jarrell Krishnamurthy, Katsnelson and Lichtenstein periodized scheme, Nested Cluster Schemes Schiller Ingersent ), causality issues, O. Parcollet, G. Biroli and GK cond-matt 0307587 (2003) RUTGERS THE STATE UNIVERSITY OF NEW JERSEY
Two paths for ab-initio calculation of electronic structure of strongly correlated materials Crystal structure +Atomic positions Model Hamiltonian Correlation Functions Total Energies etc. DMFT ideas can be used in both cases. RUTGERS THE STATE UNIVERSITY OF NEW JERSEY
LDA+DMFT V. Anisimov, A. Poteryaev, M. Korotin, A. Anokhin and G. Kotliar, J. Phys. Cond. Mat. 35, 7359 (1997). A Lichtenstein and M. Katsnelson PRB 57, 6884 (1988). n n q q The light, SP (or SPD) electrons are extended, well described by LDA. The heavy, D (or F) electrons are localized treat by DMFT. LDA Kohn Sham Hamiltonian already contains an average interaction of the heavy electrons, subtract this out by shifting the heavy level (double counting term) Kinetic energy is provided by the Kohn Sham Hamiltonian (sometimes after downfolding ). The U matrix can be estimated from first principles of viewed as parameters. Solve resulting model using DMFT. Impurity Solvers: QMC-IPT-NCA……. . THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Functional formulation. Chitra and Kotliar Phys. Rev. B 63, 115110 Ir>=|R, r> Double loop in Gloc and Wloc THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Next Step: GW+EDMFT S. Savrasov and GK. (2001). P. Sun and GK. (2002). S. Biermann F. Aersetiwan and A. Georges. (2002). P Sun and G. K (2003) W EH + W Implementation in the context of a model Hamiltonian with short range interactions. P Sun and G. Kotliar cond-matt 0312303 or with a static U on heavy electrons, without self consistency. Biermann et. al. PRL 90, 086402 (2003) THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Self-Consistency loop. S. Savrasov and G. Kotliar (2001) and cond-matt 0308053 E U DMFT THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
How good is approach ? n n It becomes exact as the coordination number increases or in the limit of infinite dimensions introduced by Metzner and Vollhardt. PRL 62, 34, (1989). How good is it in low dimensions ? Promising recent developments from theory and experiments. THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Schematic DMFT phase diagram and DOS S Lefebvre et al. PRL (2000) THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Recent Experiments support qualitative single site DMFT predictions Mo et al. , Phys. Rev. Lett. 90, 186403 (2003). Limelette et. al. (2003) Ito et. al. (1995) THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Theoretical issue: is there a Mott transition in the integer filled Hubbard model, and is it wel YES! Parcollet Biroli Kotliar cond-matt 0308577 Study frustrated t t’ model t’/t=. 9 THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Evolution of the k resolved Spectral Function n Qualitative effect, formation of hot regions! D wave gapping of the single particle spectra as the Mott transition is approached. Very strong k dependece near the trasition. U/D=2. 25 Uc=2. 35+-. 05, Tc/D=1/44 THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Ti 2 O 3 : Coulomb or Pauling C. E. Rice et all, Acta Cryst B 33, 1342 (1977) n LTS 250 K, HTS 750 K THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Ti 2 O 3. n n Isostructural to V 2 -x. Crx. O 3. Al lot of the qualitative physics of the high temperature part of the phase diagram of V 2 O 3 can be understood within single site DMFT. Is this true in Ti 2 O 3? Band Structure Calculations good metal. L. F. Mattheiss, J. Phys. : Condens. Matter 8, 5987 (1996). Unrestricted Hartree Fock calculations produce large antiferromagnetic gap. M. Cati, et. al. Phys. Rev. B. f 55 , 16122 (1997). THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
2 site-Cluster DMFT with intersite Coulomb U = 2, J = 0. 5, W = 0. 5 β = 20 e. V-1, LT structure U = 2, J = 0. 5, W = 0. 5 β = 10 e. V-1, HT structure THE STATE UNIVERSITY OF NEW JERSEY RUTGERS A. Poteryaev
Pauling and Coulomb Ti 2 O 3[S. Poteryaev S. Lichtenstein and GK condmat 0311319 ] Dynamical Goodenough. Honing picture THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Conclusion Ti 2 O 3 n n 2 site cluster DMFT describes the MIT in Ti 2 O 3. Different from V 2 O 3 where single site DMFT works well, and cluster corrections are small [A. Poteryaev] It requires the Coulomb interactions, and a frequency dependent enhancement of the a 1 g-a 1 g hopping, induced by the Coulomb interactions. [Haldane Ph. D thesis, Q Si and GK 1993 ]. Dynamical Pauling. Goodenough mechanism is able to trigger the MIT at low enough temperatures. Coulomb and Pauling synergistically cooperate. THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Pu phases: A. Lawson Los Alamos Science 26, (2000) LDA underestimates the volume of fcc Pu by 30% Predicts magnetism in d Pu and gives negative shear Core-like f electrons overestimates the volume by 30 % RUTGERS THE STATE UNIVERSITY OF NEW JERSEY
The delta –epsilon transition n The high temperature phase, (epsilon) is body centered cubic, and has a smaller volume than the (fcc) delta phase. What drives this phase transition? Having a functional, that computes total energies opens the way to the computation of phonon frequencies in correlated materials (S. Savrasov and G. Kotliar PRL 90, 056401) THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Total Energy as a function of volume for Pu (after Savrasov, Kotliar, Abrahams, Nature , 410, 793, (2001)
DMFT Phonons in fcc d-Pu C 11 (GPa) C 44 (GPa) C 12 (GPa) C'(GPa) Theory 34. 56 33. 03 26. 81 3. 88 Experiment 36. 28 33. 59 26. 73 4. 78 (after Dai, Savrasov, Kotliar, Ledbetter, Migliori, Abrahams, Science, 9 May 2003) (experiments from Wong et. al, Science, 22 August 2003)
DMFT Phonons in bcc e-Pu
Phonon entropy drives the epsilon delta phase transition n n Epsilon is slightly more delocalized than delta, has SMALLER volume and lies at HIGHER energy than delta at T=0. But it has a much larger phonon entropy than delta. Different from Cerium see Jeong et. al. condmat/0308416 n n At the phase transition the volume shrinks but the phonon entropy increases. Estimates of the phase transition following Drumont and Ackland et. al. PRB. 65, 184104 (2002); (and neglecting electronic entropy). TC ~ 600 K. THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Outlook n n Dynamical mean field theory, ” local reference “ for correlated electron systems. Analogy to FLT, DFT. The need of simpler reference frames for thinking about complex problems. Future directions: downfolding and RG, algorithmic speedups. While a general method is under construction, the extensions described in this talk, already allow to perform quantitative calculations and obtain quantitative insights. THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
Conclusion n n Introduction to DMFT and its extensions. Flexibility of a local approach. DMFT describes well the Mott transitions. Formation of hot and cold regions near FS. MIT in Ti 2 O 3 cluster DMFT. Dynamical Pauling-Coulomb mechanism. Delta-Epsilon Plutonium. Correlations and phonon entropy. THE STATE UNIVERSITY OF NEW JERSEY RUTGERS
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