Generation of Walkers

From Zori Wiki

The generation of walkers in Zori tends to be very simple and rapid once you have good psi and orbitals files from the previous trial wave function creation step. A sample input file create.xml for the creation of walkers is included. Modify the create.xml file so that the number of “Particles” is equal to the number of electrons and that the “TargetEnergy” is reasonably close to energy of you trial wave function. In this section examples of how to create single and multiprocessor walker files (both XML and HD5 formats) in the LAM MPI environment is described.

Description of important tags in create.xml input file.

WalkersPerProcessor = self-explanatory: how many walkers per processor will be produced.

TargetEnergy = walkers produced will be distributed around this Energy. It should correspond approximately to the energy of the trial wave function.

Tolerance = this parameter controls the tolerance on the acceptance of generated configurations when their energies deviate from the TargetEnergy. Setting this parameter too small increases the time needed to generate the walker file. Setting it too large produces high-energy configurations that may get stuck in the QMC calculation or produce "cannot compose determinant" errors.

Dimensions = Currently only 3-D is implemented in Zori

Particles = this usually corresponds to the number of electrons in the atom or molecule

XML format walkers

The command to create the walkers in XML format on a single processor and store them in a file called walkers-0.xml is for example:

zori  -i create.xml -p hno-psi.xml -w walkers -n 

The "-n" option is necessary so that Zori will not attempt to read walkers from a nonexistent walkers file. The "-w" option causes the walkers to be stored in a file with the prefix ("walkers") specified followed by the processor number ("-0.xml").

To modify this command for Zori to generate, for example, 6 walker files for a 6 processor calculation just preface the zori command by the mpirun command that is specific for your version of mpi. For LAM-MPI the command would be:

mpirun -np 6 zori -i create.xml -p hno-psi.xml -w walkers -n

This would generate the files walker-0.xml, walker-1.xml, walker-2.xml, walker-3.xml, walker-4.xml, walker-5.xml.

Be careful: The order of the command-line options does matter :( Try to add the -n option to the end) this is bug #6 in the database and we are working n it as of 5.30 PM March 31st, 2005.

HDF format walkers

To create your walkers in HDF5 format

zori  -H -i create.xml -p hno-psi.xml  -w walkers.hdf5 -n > create.out 

If you want to interconvert between HDF5 and XML walker files, refer to Walker Format Conversion

Now that you have walkers you are ready to proceed with a VMC calculation.

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