how can I restart run process from a specially step,
for example:my computer is turned off and run stopped in 400000th
step,but I can't start that from 400000th step,and begin it from the
please guide me

In order to restart a simulation, you need either a dump file or a restart file.


That really depends. You will need to have the velocities and positions of all atoms at that specific time step.
If you wrote out restart files every now and then it is easy, you can just use read_restart.
If you wrote out data files every now and then the same applied but you use read_data.
If you wrote out a dump file you could write a script that hacks the latest time step from that dump file into a data file that you can use with read_restart.

If you have no way of accessing atom positions and velocities at that particular time step then there is no way to restart from a specific time step; you will have to repeat your simulation from the start.