# Why does a particle rotate

Dear Axel,

Thank you for the suggestions.
If I use the "zero" option of velocity, do I still need to define a initial
velocity by "create" option? Like:
velocity all create 300 1178591
velocity all zero angular
Or just use "zero" option. Sorry about my confusion here.

well, *think* about it. and then *try* it and observe before asking
such a (trivial) question. you can save yourself a lot of
embarrassment this way.

perhaps start by answering this question: how would the velocity
command know *which* temperature you want that sample to have?

axel.

Dear Axel,

The velocity is calculated based on an initial temperature and a random number that set in velocity command. If we do not use create option, then initial temperature is 0 and velocity is also 0. So I think it is necessary to use both of them ( velocity all create 300 1178591, velocity all zero angular) if I want to simulate a particle without angular velocity at the beginning.

Best regards,
Leo

Dear all,

I used zero option in velocity command to make the initial angle velocity as zero, so the particle does not rotate but just vibrate. Since the overall kinetic energy is decreased, then the calculated temperature is also decreased, which means the calculated melting point without rotation is supposed to be smaller than that with rotation. However, it is contradictory from my result. I think it might be related to the pressure effect as the pressure would be different for these two cases.

Best regards,
Cong (Leo) Dai

Dear all,

I used zero option in velocity command to make the initial angle velocity as
zero, so the particle does not rotate but just vibrate. Since the overall
kinetic energy is decreased, then the calculated temperature is also
decreased, which means the calculated melting point without rotation is
supposed to be smaller than that with rotation. However, it is contradictory
from my result. I think it might be related to the pressure effect as the
pressure would be different for these two cases.

what result from what is contradicting with what? there is far too
much context missing here to give any kind of meaningful answer
AFAICT.