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run command

Syntax:

run N keyword values ... 

Examples:

run 10000
run 1000000 upto
run 100 start 0 stop 1000
run 1000 pre no post yes
run 100000 start 0 stop 1000000 every 1000 "print Protein Rg = $r"
run 100000 every 1000 NULL 

Description:

Run or continue dynamics for a specified number of timesteps.

When the run style is respa, N refers to outer loop (largest) timesteps.

A value of N = 0 is acceptable; only the thermodynamics of the system are computed and printed without taking a timestep.

The upto keyword means to perform a run starting at the current timestep up to the specified timestep. E.g. if the current timestep is 10,000 and "run 100000 upto" is used, then an additional 90,000 timesteps will be run. This can be useful for very long runs on a machine that allocates chunks of time and terminate your job when time is exceeded. If you need to restart your script multiple times (reading in the last restart file), you can keep restarting your script with the same run command until the simulation finally completes.

The start or stop keywords can be used if multiple runs are being performed and you want a fix command that changes some value over time (e.g. temperature) to make the change across the entire set of runs and not just a single run. See the doc page for individual fixes to see which ones can be used with the start/stop keywords. The pair_style soft potential also changes its pair potential coefficients in this manner.

For example, consider this fix followed by 10 run commands:

fix	     1 all nvt 200.0 300.0 1.0
run	     1000 start 0 stop 10000
run	     1000 start 0 stop 10000
...
run	     1000 start 0 stop 10000 

The NVT fix ramps the target temperature from 200.0 to 300.0 during a run. If the run commands did not have the start/stop keywords (just "run 1000"), then the temperature would ramp from 200.0 to 300.0 during the 1000 steps of each run. With the start/stop keywords, the ramping takes place over the 10000 steps of all runs together.

The pre and post keywords can be used to streamline the setup, clean-up, and associated output to the screen that happens before and after a run. This can be useful if you wish to do many short runs in succession (e.g. LAMMPS is being called as a library which is doing other computations between successive short LAMMPS runs).

By default (pre and post = yes), LAMMPS creates neighbor lists, computes forces, and imposes fix constraints before every run. And after every run it gathers and prints timings statistics. If a run is just a continuation of a previous run (i.e. no settings are changed), the initial computation is not necessary; the old neighbor list is still valid as are the forces. So if pre is specified as "no" then the initial setup is skipped, except for printing thermodynamic info.

IMPORTANT NOTE: If your input script changes settings between 2 runs (e.g. adds a fix or dump or compute or changes a neighbor list parameter), then the initial setup must be performed. LAMMPS does not check for this, but it would be an error to use the pre option in this case.

If post is specified as "no", the full timing summary is skipped; only a one-line summary timing is printed. Note that if pre is set to "no" for the 1st run LAMMPS performs, then it is overridden, since the initial setup computations must be done.

The every option provides a means of interleaving LAMMPS runs with a command. This can be a short-hand abbreviation to avoid listing a long series of runs in your input script. Or it can be useful for invoking a command that wraps some other code (e.g. as a library) to perform a computation periodically during a long LAMMPS run. See this section of the documentation for ideas about how to couple LAMMPS to other codes.

N total steps are simulated, in shorter runs of M steps each. After each M-length run, the command is invoked. If the command is specified as NULL, no command is invoked. Thus these lines:

variable q equal x[100]
run 6000 every 2000 "print Coord = $q" 

are the equivalent of:

variable q equal x[100]
run 2000
print Coord = $q
run 2000
print Coord = $q
run 2000
print Coord = $q 

which does 3 runs of 2000 steps and prints the x-coordinate of a particular atom between runs. Note that the command can contain variables of style equal which will be evaluated each time the command is invoked.

If the pre and post options are set to "no" when every is used, then the 1st run will do the full setup and the last run will print the full timing summary, but these operations will be skipped for intermediate runs.

Restrictions: none

Related commands:

minimize, run_style, temper

Default:

The option defaults are start = the current timestep, stop = current timestep + N, pre = yes, and post = yes.