This specifies the maximum run time for the job. If run_time is
greater than zero, the job will, if possible, exit cleanly before this
time in seconds has elapsed, leaving as little unused time as possible.
Clean termination before run_time cannot be guaranteed, and the
shortest operation which can be timed is an electronic minimisation
or a single molecular dynamics, geometry optimisation or phonon step.
If
no time limit will be imposed on the run.
The default value of this parameter is 0.