The CONTROL file is read by the subroutine SIMDEF and defines the control variables for running a DL_POLY_2 job. It makes extensive use of directives and keywords. Directives are character strings that appear as the first entry on a data record (or line) and which invoke a particular operation or provide numerical parameters. Also associated with each directive may be one or more keywords, which may qualify a particular directive by, for example, adding extra options. Directives can appear in any order in the CONTROL file, except for the finish directive which marks the end of the file. Some of the directives are mandatory (for example the timestep directive that defines the timestep), others are optional.
This way of constructing the file is very convenient, but it has inherent dangers. It is, for example, quite easy to specify the same directive more than once, or specify contradictory directives, or invoke algorithms that do not work together. By and large DL_POLY_2 tries to sort out these difficulties and print helpful error messages, but it does not claim to be foolproof. Fortunately in most cases the CONTROL file will be small and easy to check visually. It is important to think carefully about a simulation beforehand and ensure that DL_POLY_2 is being asked to do something that is physically reasonable. It should also be remembered that the present capabilites the package may not allow the simulation required and it may be necessary for you yourself to add new features.
An example CONTROL file appears below. The directives and keywords appearing are described in the following section.
Title Record: Example CONTROL file for DL_POLY
# define the state point
temperature 300.0
# simulation length and equilibration
steps 2000
equilibration steps 1000
scale every 5 steps
timestep 0.0005 ps
multiple timestep 1 steps
# specify cutoffs
cutoff 7.6 angstrom
delr 0.5 angstrom
# print controller
print every 100 steps
# rdf options
rdf sampling every 10 steps
print rdf
# job time and permitted wind-up time
job time 21000 seconds
close time 200 seconds
# forces options
ewald sum 0.48 6 6 6
cap forces in equilibration mode 2000 kT/A
# ensemble options
ensemble nve (default option)
# statistics controls
stats every 2000 steps
stack 100 deep
# trajectory dumping controls
trajectory nstraj 1 istraj 50 keytrj 0
finish