Hi Dear lammps users

I have confused with the basic command of lammps.

For example in the following commands in the “flow” example of lammps:

Compute mobile flow temp

Velocity flow create 1.10 482748 temp mobile

As we know, the “velocity” command sets initial velocities in special temperature that is computed with “compute” command.

Now my question is this: for computing the temperature of system we need velocity according to kinetic energy…. so how can “compute” command generate temperature while the initial velocities have not produced yet?

Thanks for any discussion

Hi Dear lammps users

I have confused with the basic command of lammps.

For example in the following commands in the "flow" example of lammps:

Compute mobile flow temp

Velocity flow create 1.10 482748 temp mobile

As we know, the "velocity" command sets initial velocities in special temperature that is computed with "compute" command.

No, it does not.

Now my question is this: for computing the temperature of system we need velocity according to kinetic energy…. so how can "compute" command generate temperature while the initial velocities have not produced yet?

The velocity command just sets the velocities from random numbers

following a given distribution. All it needs to know for that are the

number of degrees of freedom and the atom masses. Please look up in

your MD textbook how temperature is being calculated in atomistic MD

simulations.

Axel

thanks a lot.

I have another question.

in this way, why the temperature computed with "compute" command was

used in"velocity command" via "temp" keyword? and what does it mean?

thanks

Elena

thanks a lot.

I have another question.

in this way, why the temperature computed with "compute" command was

used in"velocity command" via "temp" keyword? and what does it mean?

this is easiest found out by reading the source code.

as i wrote in my previous response, one needs to know

the number of degrees of freedom in order to compute

the (instantaneous) temperature and the velocity command

does this by *first* assigning random velocities according to

the selected distribution and then using the temperature

computed from this to scale the velocities to exactly

produce the desired temperature.

check out the Velocity::create() method in velocity.cpp

starting at line 149.

axel.