Sorry, we missed to include this in the manual. We are working on a "parallel guide", but for now, I can just copy here the docstring, and hopefully you can figure things out. In short, this option is only relevant for NEB calculations and global optimizations (crystal prediction).
def __init__(self, processes_per_neb_image=None, processes_per_individual=None):
"""
Constructor.
@param processes_per_neb_image : The number of processes that should be used to
calculate each NEB image. A value of None indicates
that the value will be determined automatically.
@type : int
@default : Automatically determine the number of processes that
should be used to calculate a single configuration
in parallel based upon the total number of MPI
processes.
@note : This argument can be set on the command line with
the option "--processes-per-neb-image=<number>".
The number of processes per configuration specified
on the command line takes precedence over the number
specified here.
@param processes_per_individual : The number of processes that should be used to
calculate each individual in the global optimization
calculation. A value of None indicates that the value
will be determined automatically.
@type : int
@default : Automatically determine the number of processes that
should be used to calculate a single configuration
in parallel based upon the total number of MPI
processes.
"""
