temp/profile temperature definition

Dear all,

I am computing the temperature of a Poiseuille flow by means of compute temp/profile (in order to substract the spatially-averaged center-of-mass streaming velocity). In the doc page it is explained how the temperature is related to the kinetic energy in this case:

“After the spatially-averaged velocity field has been subtracted from each atom, the temperature is calculated by the formula KE = (dim/2 N - dimNxNy*Nz) k T, where KE = total kinetic energy of the group of atoms (sum of 1/2 m v^2), dim = 2 or 3 = dimensionality of the simulation, N = number of atoms in the group, k = Boltzmann constant, and T = temperature.”

Is it possible that there is a little mistake related to the number of degrees of freedom in the temperature expression? I would say that the right form would be KE = (dimN-dimNxNyNz)*k T/2. That is, the factor (1/2) multiply also the degrees of freedom per bin.

Thanks! And I’m sorry if this point has already been explained.

Carlos Espejo

Yes, that is correct. We will change it.


Actually, I think that doc page formula is consistent with

the code which has this comment:

// subtract additional d*Nbins DOF, as in Evans and Morriss paper

Within the last ~year someone called our attention to that

issue discussed in the paper, and we subtracted dim DOF per

bin as a result. You can probably search the maillist

archives for the post. If I recall the post had plots showing

the difference it makes.


oops I was wrong, Aidan and Carlos are right. The

code is doing the right thing, but the doc

page needs to be changed.