confusion with strain rate units
sphCow opened this issue · comments
Before I begin, thanks a lot for making these tutorials available. I've a doubt here. In tutorial 3, after the initial equilibration, the simulation box is deformed
in the x-direction at a strain rate of 10^10 1/s
That is implemented in the LAMMPS script in the following lines
units metal
...
timestep 0.001 #in picosecond
...
variable srate equal 1.0e10
variable srate1 equal "v_srate / 1.0e12"
fix 2 all deform 1 x erate ${srate1} units box remap x
How do you calculate the factor of 1.0e12 ? Isn't the timestep dt involved here in some way?
Hello! I think it is because the pico prefix value is 1e-12. So dividing the srate by 1e12 (or multiplying by 1e-12) you are converting srate in sec to pico sec. So your total time for the calculation is 10^10 seconds (1e10) and you are having the time step be a pico second. ? Hopefully the writer of this code can verify, but those are my thoughts.
Thanks! I went ahead and added this to the FAQ section. Claireb5112, you were almost right on all accounts. It is a unit conversion. The total time isn't 10^10, that is just the strain rate; and the timestep isn't picosecond, but rather 0.001 picosecond (femtosecond, 1e-15 s). I added a little more explanation in the FAQ.