# time of my stimulation !

hi guys…
I usually simulate without dimension and set lj for unit command in my input lammps’s code…
now i want to use my output and plot them but i can’t understand what is the simulation time?(I do’nt know where i set the time of my stimulation?) …to calculate velocity with si unit for example m/s…
maintain i write this command in part of code:
unit lj
timestep 0.005

fix 8 flow ave/spatial 2 5000 10000 y center 0.05 vx units reduced file vel.profile

run 100000

and in manual i read: “For style lj these are dt = 0.005 tau” and “time = tau, where tau = t* = t (epsilon / m / sigma^2)^1/2”
i want to know what is t? How to be considered?

t is the real (non-scaled) time. It can be in any unit you choose as long as you’re consistent in choosing m, sigma and epsilon, such that "tau = (msigma^2/epsilon)^1/2" give you the same unit of time. It should be t = t / tau maybe that 'tau = ’ before t* is a typo in the manual, any comment?

hth,
Kasra.
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t is the real (non-scaled) time. It can be in any unit you choose as long as
you're consistent in choosing m, sigma and epsilon, such that "tau =
(m*sigma^2/epsilon)^1/2" give you the same unit of time. It should be t* = t
/ tau maybe that 'tau = ' before t* is a typo in the manual, any comment?

the expression in the manual makes sense if you read it as:

t <times> (epsilon / m / sigma^2)^1/2

granted it is a bit confusing, but please also see the following lines
where the same applies. because of the convention to use t*, it would
be even more confusing to use a '*' to indicate multiplication.

axel.

Definitely...also isn't that "tau=" in the manual a typo?
tau = t* = t (epsilon / m / sigma^2)^1/2

Kasra.

yes, it should just be:

time = tau, where t* = t (eps …)^1/2

I.e. t* is in unitless units of tau.

Hadn’t noticed it - will change it

thanks,
Steve