That is, the Tdamp is 100 and the Pdamp is 1000 time steps, respectively. And, it could also assume that a time unit of metal in current Lammps version is ps (picosecond), right ??
However, recently my one coleague told me that a time unit of metal in current Lammps version was fs (ficosecond), so above the command should be wr-written as follows
If you read the manual carefully you will see that Tdamp and Pdamp have time units. In the case of metal units they are ps.
If you want Tdamp to be 100 time steps the documentation gives you an easy way to do it, namely: fix 1 all nvt temp 300.0 300.0 $(100.0*dt) dt will by substituted by the current time step and so the Tdamp will be exactly 100 time steps.
So, to answer your question, the second command is correct, since you are doing 100*dt and 1000*dt manually.