Another important facility of the FCIQMC module is the ability to write out restart files (POPSFILEs), detailing the
specific number and distribution of the walkers throughout the space. These files can then be copied between systems
if desired, and the calculation continued from where it left off. Writing out these POPSFILEs is recommended in case further accuracy is
required at a later stage. If the previous FCIQMCStats file is also present in the working directory of the restarted calculation,
then the new data obtained will be simply appended to the end of the previous FCIQMCStats file.
Two files are required to restart a
calculation: POPSFILEHEAD and POPSFILEBIN. Options to control their use include:
- If this option is specified, then the required POPSFILEs are written out in the event
of a clean exit from the calculation, either via the ITERATIONS or TIME options, or the CHANGEVARS facility.
In addition, the POPSFILEs are written out in iteration intervals specified by the value given. If a value of zero is
given, the POPSFILEs will only be written out at the end of the calculation.
- This option will write out POPSFILEs at time intervals of value hours, as well as
the end of the calculation.
- This option will ensure that if multiple POPSFILEs are written out in one simulation,
they will not overwrite previous versions, but rather append incrementing numerical suffixes to the filenames, i.e. POPSFILEHEAD.x.
These must be renamed/linked as files called simply POPSFILEHEAD and POPSFILEBIN for reading in for subsequent calculations.
- This option must be present in order to read back in walkers from POPSFILEs.
- By default, the simulation will resume in variable shift mode. This option will
resume the calculation in variable shift mode.