# units problem

Dear All,

I just found out a units problem—maybe it is my problem but I have tested a very simple example.

the units I am using is “metal”, so the velocity unit is Angstroms/picosecond, distance unit is Angstroms and time unit is picosecond. Then I specify an atom at location [1 1 1] and specify “fix move” for the atom is " fix … move 0 0 -1 units box". The simulation is to run 100 steps, in which I suppose the atom will move toward z direction 1*100=100 Angstromes. However, this atom only moves 0.1 Angstrome as the final position is [1 1 0.9]. This is a test simulation so nothing is physically meaningful. All I wanna see is this atom moves at the speed I want to see. Please correct me if I have made some problem and thank you all.

Regards,
Mengyu

Dear Mengyu,

Default timestep is 0.001 psec for units = metal. So 0.001*100=0.1 Angstroms

See timestep <http://lammps.sandia.gov/doc/timestep.html> command for
details.

Grigory Smirnov

2012/4/22 Mengyu Lan <[email protected]...>