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c CCLRC
Section 5.1
user uses only the bold part of these directives.
Table 5.1: Internal Trajectory/Defects File Key
keytrj
meaning
0
coordinates only in file
1
coordinates and velocities in file
2
coordinates, velocities and forces in file
5.1.1.3
Further Comments on the CONTROL File
1. A number of the directives (or their mutually exclusive alternatives) are mandatory:
(a) timestep or variable timestep: specifying the simulation timestep
(b) temp or zero: specifying the system temperature (not mutually exclusive).
(c) ewald sum or ewald precision or coul or shift or distan or reaction or no elec:
specifying the required coulombic forces option
(d) cut: specifying the short range forces cutoff.
2. Some directives are optional. If not specified DL POLY 3 will take default values if necessary.
The defaults are specified above in the list of directives.
3. The variable timestep (or also timestep variable) option requires the user to specify
an initial guess for a reasonable timestep for the system (in picoseconds). The simulation
is unlikely to retain this as the operational timestep however, as the latter may change in
response to the dynamics of the system. The option is used in conjunction with the default
values of maxdis (0.03 °
A) and mindis (0.10 °
A), which can also be optionally altered if used
as directives (note the rule that maxdis > 2.5 mindis applies). These distances serve as
control values in the variable timestep algorithm, which calculates the greatest distance a
particle has travelled in any timestep during the simulation. If the maximum distance is
exceeded, the timestep variable is halved and the step repeated. If the greatest move is less
than the minimum allowed, the timestep variable is doubled and the step repeated. In this
way the integration timestep self-adjusts in response to the dynamics of the system.
4. The job time and close time directives are required to ensure a controlled close down
procedure when a job runs out of time. The time specified by the job time directive indicates
the total time allowed for the job. (This must obviously be set equal to the time specified to
the operating system when the job is submitted.) The close time directive represents the
time DL POLY 3 will require to write and close all the data files at the end of processing.
This means the effective processing time limit is equal to the job time minus the close time.
Thus when DL POLY 3 reaches the effective job time limit it begins the close down procedure
with enough time in hand to ensure the files are correctly written. In this way you may be
sure the restart files etc. are complete when the job terminates. Note that setting the close
time too small will mean the job will crash before the files have been finished. If it is set too
large DL POLY 3 will begin closing down too early. How large the close time needs to be to
ensure safe close down is system dependent and a matter of experience. It generally increases
with increasing simulation system size.
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