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Contents 1 ALPS/DMFT workshop, December 7-9, 2006, Göttingen 1.1 Meeting Notes 1.1.1 Thursday afternoon 1.1.2 Friday Morning 1.1.3 Friday Afternoon 1.1.4 Saturday Morning

ALPS/DMFT workshop, December 7-9, 2006, Göttingen

Meeting Notes

Thursday afternoon

• In attendance:
  • Frithjof Anders (arrival around 15:45)
  • Sebastian Fuchs
  • Emanuel Gull
  • Andreas Honecker
  • Hunpyo Lee
  • Gang Li
  • Munehisa Matsumoto
  • Reinhard Noack (arrival shortly before 17:30)
  • Robert Peters
  • Michael Potthoff
  • Thomas Pruschke
  • Ulrich Schollwöck

• Schedule
• start at 15:00
• Review of existing ALPS DMFT framework by Emanuel Gull
• Issues:

1. Discretization of energy/time axis
   Cases:

1. G(tau_i), tau_i=i beta/N
2. G(omega_i) for some given (non-equidistant) omega_i
3. (a_n,b_n), n=0, 1, ... for continued fraction expansion

proposed solution: map<double, complex>, meaning a tag in XML
2. Interface for Hamiltonian solvers
3. Interface for complex ordered phases
4. Self-energy functionals by Michael Potthoff (not urgent)
5. Analytic continuation (maximum entropy etc.) (not urgent)
6. Measurements of two-particle Green's functions

Friday Morning

• Start at 10:30, in attendance: same as Thurs. afternoon
• General ALPS talk for those that are new to ALPS (Reinhard)
  • Comments/Discussion:
    • ALPS 2.0: More flexible scheduler appropriate for DMFT (and parallel tempering in QMC)
    • Band structure interface: contact other groups (e.g., O Anderson, www.abinitio.org, ...)
    • Documentation: migrate more fully from old html web pages, make link more visible?
• DMFT-QMC blackboard discussion (Thomas P.)
  • construction of effective Hamiltonian (for DMRG, NRG, ED)
  • Bottom line for DMFT-loop of ALPS: loop: Solver->sigma(z)->ALPS->G_0(z)->Solver
  • Numerical stability of DMFT loop - precision of numbers, rounding errors
    • ALPS box: should contain stabilization (e.g., mixing old & new solutions, spin averaging)
    • What is saved at each loop interation?
    • sigma(z), G_0(z) data elements can be more general (matrices) for DCA, CDMFT, ...
    • Clusters/multiple orbitals generated from model/lattice library descriptions

Friday Afternoon

• Talks in SFB Workshop
  • Michael P.: Nonperturbative Conserving Appriximations for Systems of Strongly Correlated Electrons
  • Uli S.: Recent Trends in the DMRG
  • Emanuel G.: Continuous Time Solvers for DMFT
  • Frithjof A.: DMFT and Numerical RG at Finite Temperature: Prospects and Challenges

Saturday Morning

• Start at 09:30
• In attendance:
  • Frithjof Anders
  • Sebastian Fuchs
  • Emanuel Gull
  • Andreas Honecker
  • Hunpyo Lee
  • Gang Li
  • Munehisa Matsumoto
  • Reinhard Noack
  • Robert Peters
  • Thomas Pruschke
• Analytic continuation (stochastic sampling) status: Sebastian F.
• Hilbert transform for arbitrary D.O.S. (e.g., from LDA)
  • Tetrahedron integration
  • Poles, interpolation
  • -> Fortran 77 code from Anisimov group -> ALPSification?
  • Multiband case: Green functions matrices; cases:
    • H(k) diagonal in orbital indices
    • H(k)-> diagonal, sigma(z) not diagonal
• Immediate Goal: flexible data formats, initial support of usual (simple) D.O.S.'s
• Self-consisitency condition depends on model, e.g., periodic Anderson model
• Specification of ordered phases: fits into general multiorbital scheme, e.g., magnetic supercell?
  • issue: need information about lattice structure beyond D.O.S. -> adapt input to Hilbert transform
• Generalization of XML definitions for Solver->Hilbert transforms
  • VECTOR->MAP
  • tags for spin, orbital, type of order, e.g., paramagnetic

• Closing of workshop at 11:30

Thanks to Reinhard for a major fraction of these notes.