# May compute temperture have little problem?

Hi everyone,
I simulate Kremer-Greast model for polymer melts, and use DPD instead of langevin equation

For some reason, I freeze the end of polymer(set velocity 0 at first), then run the program, just use set force commond

I also calculte the tempeture(i.e. compute temp command), and the group is all free monomers, then output the temperture

In my system, there are 13200 monomers, and the chain length is 25, so there are 12144 free monomers

It is amzing that temp is 0.92 not 1.0, just 12144/13200=0.92!

I output the velocity of all monomers, calculate the temperture of free monomer, and answer is right

So, I think that compute temp use wrong number.

Because I use fortran not C++, I could not check this little problem

Best wishes

Yongjin Ruan

Hi everyone,
I simulate Kremer-Greast model for polymer melts, and use DPD instead of langevin equation

For some reason, I freeze the end of polymer(set velocity 0 at first), then run the program, just use set force commond

I also calculte the tempeture(i.e. compute temp command), and the group is all free monomers, then output the temperture

In my system, there are 13200 monomers, and the chain length is 25, so there are 12144 free monomers

It is amzing that temp is 0.92 not 1.0, just 12144/13200=0.92!

I output the velocity of all monomers, calculate the temperture of free monomer, and answer is right

So, I think that compute temp use wrong number.

Because I use fortran not C++, I could not check this little problem

...and because you do not provide your input deck, neither can we
check what you did.

considering how many people use LAMMPS and the fact that the
simulation setup sounds similar to quite a few of them do, it is very
unlikely that there is an error in LAMMPS (people would notice) and
very likely, that you did something wrong.

axel.

Hello,

See the documentation of compute temp to see how it is computed
http://lammps.sandia.gov/doc/compute_temp.html

and the option to set the number of degrees of freedom
http://lammps.sandia.gov/doc/compute_modify.html

If that still does not help you, let us know. The documentation does not refer
to C++.

Regards,

Pierre