Further Comments on the CONTROL File

1. A number of the directives (or their mutually exclusive alternatives) are mandatory:
   1. timestep: specifying the simulation timestep;
   2. temp or zero : specifying the system temperature (not mutually exclusive);
   3. ewald sum or ewald precision or spme sum or spme precision or hke sum or hke precision or coul or shift or distan or reaction or no elec: specifying the required coulombic forces option;
   4. cut and delr: specifying the short range forces cutoff and Verlet strip;
   5. prim: specifying primary forces cutoff (if mult$>$2 only).
2. 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_2 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_2 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_2 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 the job size.
3. The starting options for a simulation are governed by the keyword restart. If this is not specified in the CONTROL file, the simulation will start as new. If specifed, it will either continue a previous simulation (restart) or start a new simulation with initial temperature scaling of the previous configuration (restart scale). Internally these options are handled by the integer variable keyres, which is explained in table 4.1.
4. The various ensemble options (i.e. nve, nvt ber, nvt evans, nvt hoover, npt ber, npt hoover, nst ber, nst hoover) are mutually exclusive, though none is mandatory (the default is the NVE ensemble). These options are handled internally by the integer variable keyens. The meaning of this variable is explained in table 4.2.
5. The force selection directives ewald sum, ewald precision, reaction, coul, shift, dist, no elec and no vdw are handled internally by the integer variable keyfce. See table 4.4 for an explanation of this variable. Note that these options are mutually exclusive.
6. The choice of reaction field electrostatics (directive reaction) requires also the specification of the relative dielectric constant external to the cavity. This is specified in the eps directive.
7. DL_POLY_2 uses as many as three different potential cutoffs. These are as follows:
   1. rcut - this is the universal cutoff. It applies to the real space part of the electrostatics calculations and to the van der Waals potentials if no other cutoff is applied;
   2. rvdw - this is the user-specified cutoff for the van der Waals potentials. If not specified its value defaults to rcut;
   3. rprim - this is used in the multiple timestep algorithm to specify the primary atom region (see section 2.5.7). It has no meaning if the multiple timestep option is not used.
8. Some directives are optional. If not specified DL_POLY_2 will take default values if necessary. The defaults appear in the above table.
9. The zero directive, enables a zero temperature simulation. This is intended as a crude energy minimizer to help relax a system before a simulation begins. It should not be thought of as a true energy minimization method.
10. The DL_POLY_2 multiple timestep option is invoked if the number appearing with the mult directive is greater than 2. This number (stored in the variable multt) specifies the number of timesteps (the multi-step) that elapse between partitions of the full Verlet neighbour list into primary and secondary atoms.
11. If a multiple time-step is used, (i.e. multt$>$2), then statistics for radial distribution functions are collected only at updates of the secondary neighbour list. The number specified on the rdf directive (the variable nstbgr) means that RDF data are accumulated at intervals of nstbgr$\times$multt timesteps.
12. As a default, DL_POLY_2 does not store statistical data during the equilibration period. If the directive collect is used, equilibration data will be incorporated into the overall statistics.
13. The directive delr specifies the width of the border to be used in the Verlet neighbour list construction. The width is stored in the variable delr. The list is updated whenever two or more atoms have moved a distance of more then delr/2 from their positions at the last update of the Verlet list.

Table 4.1: Internal Restart Key

keyres	meaning
0	start new simulation from CONFIG file,
	and assign velocities from Gaussian distribution.
1	continue current simulation
2	start new simulation from CONFIG file,
	and rescale velocities to desired temperature

Table 4.2: Internal Ensemble Key

keyens	meaning
0	Microcanonical ensemble (NVE)
1	Evans NVT ensemble
2	Berendsen NVT ensemble
3	Nosé-Hoover NVT ensemble
4	Berendsen NPT ensemble
5	Nosé-Hoover NPT ensemble
6	Berendsen N $\mbox{$\underline{\underline{\bf\sigma}}$}$T ensemble
7	Nosé-Hoover N $\mbox{$\underline{\underline{\bf\sigma}}$}$T ensemble
8	Potential of mean force (NVE) ensemble

Table 4.3: Internal Trajectory File Key

keytrj	meaning
0	coordinates only in file
1	coordinates and velocities in file
2	coordinates, velocities and forces in file

Table 4.4: Non-bonded force key

keyfce	meaning
odd	evaluate short-range potentials and electrostatics
even	evaluate Electrostatic potential only
Electrostatics are evaluated as follows:
0 , 1	Ignore Electrostatic interactions
2, 3	Ewald summation
4, 5	distance dependent dielectric constant
6, 7	standard truncated Coulombic potential
8, 9	truncated and shifted Coulombic potential
10,11	Reaction Field electrostatics
12,13	SPME electrostatics
14,15	Hautman-Klein Ewald electrostatics
keyfce = 0 means no non-bonded terms are evaluated.
keyfce = 1 means only short-range potentials are evaluated.

Users are advised to study the example CONTROL files appearing in the data sub-directory to see how different files are constructed.