Some questions about atom velocity and position

Hello, Steve,

Thank you for your answering so fast.
I was not time integrating the atoms with something like fix nve,
and I used "fix temp/rescale" command.

I understood it's not an adequate command.
Then, I used time integrating command as below,
"fix 1 all nvt temp 300.0 300.0 0.001" (timestep:0.001[ps])

,and I have an error message "ERROR: Lost atoms: original 1760801
current 1760414" on the way of running.
In addition, the system temperature does not become stable around 300K

I can't understand what's happening in my simulation

Thanks for your helping.