QMCPACK Features 2008-10-29

From QMCPACK

Contents 1 Summary 2 QMC Drivers 3 QMC WaveFunctions 4 QMC Hamiltonians 5 Tools 6 Todo (Urgent) 7 Plans

[edit] Summary

• Subversion repository

Developers (valid user id and password are required)
 svn co http://cms.mcc.uiuc.edu/svn/qmcpack-dev/trunk qmcpack-dir

• Developer and user profile
  • Active developers: J. Kim, K. Esler, J. McMinis, B. Clark, J. Gergely, C. Yang
  • Other contributors (early): S. Chiesa, K. Delaney, J. Vincent
  • External collaborators: P. Kent, F. Roboredo, M. Einbach (ORNL)
• More tests and runs were done, which confirmed the "correctness" of the implementation.
• Overall performance improved by using einspline and others.
• The classes for optimization are rewritten to be able to do energy optimization using analytic derivatives.
  • Derivatives are implemented.
  • However, currently we use finite-difference methods to calculate the forces on the optimizable variables.
  • Bugs seem to exist to exclude certain variables during the optimization.
  • Hard-to-optimize cases exist.
• The method to generate samples for optimization and DMC is changed.
  • Use <parameter name="samples">2560</parameter>
    • within the optimization block
    • the vmc block preceding DMC blocks.
• Introduce warm-up steps for both VMC and DMC
  • Use <parameter name="warmupSteps">1000</parameter>
  • VMC discards the data (you don't even see them).
  • DMC keeps the record in *.dmc.dat file. Be sure to exclude the data for analysis.
• Running multiple configurations or twists in a job is possible.
  • Occasionally crashes. Working on finding out the problems.
• DMC parallel performance is good.

[edit] QMC Drivers

• VMC/DMC/RMC
• Variational optimization of Jastrow Functions

[edit] QMC WaveFunctions

• Fermion wavefunctions
  • Slater deetrminants. These one-particle orbitals (derived from SPOSetBase (Single Particle Orbital Set Base) can be used:
    • Bspline using einspline library
    • Bspline using internal classes
    • Molecular Orbitals: STO, GTO and numerical
    • PlaneWave
    • Homogeneous Electron Gas
  • BCS orbital with Molecular Orbitals
• Jastrow Functions
  • One-Body Jastrow
  • Two-Body Jastrow
  • Three-Body Jastrow
  • Standard scaling functions for N-body Jastrow
    • Pade
    • Bspline
    • WM (Wagner-Mittas) : do not use it unless Pade or Bspline does not work.
  • Other special-purpose scaling functions are available and check with the authors.

[edit] QMC Hamiltonians

• Physical Hamiltonian: sum of these is a local energy of a walker.
  • Kinetic operator
  • Coulomb potentials with/without periodic boundary conditions
  • Local pseodupotentials
  • Non-local pseudopoentials

The division of local and non-local pseudopotentials is done internally based on the 
designation of the local channel in a pseudopotential input file.

• Estimators (don't get confused with EstimatorManager)
  • They don't contribute to the local energy but evaluated whenever a new configuration is accepted.
  • They are mostly experimental.
  • Examples are force, pressure

[edit] Tools

• Conversion tools from pwscf, Gaussian and GAMESS XML
• Conversion tools from Casino files
• Pseudopotential file generations: OPIUM will have a tool.

[edit] Todo (Urgent)

• Documetation!! + technical paper
• Test suites
• Energy optimization
• Backflow wavefunctions
• Rigorous tests and applications of the Fixed-phase DMC
• Bug fixes for the single-precision build
• Improvement management of chain jobs
  • Does not work nicely, when the completion time for the QMC blocks per MPI group is different.
  • Chain many input files to run one after another, e.g., MC samples for water, until your job is terminated.
• Optimization using twist-averages values
• Tools, web sites ....

[edit] Plans

Some of them are really experimental and should live in a branch until its usefulness is proven.

• GPU implementation
• More vectormization and SIMDizing
• Boost integration: mpi, serialization, i/o
• Threading with Intel Threading Block (TBB)

Note to developers