[lammps-users] fix heat problem

Dear all,

I want to add and subtract some energy to a system by using of fix heat
command. I see a temperature gradient is created but total energy and
mean temperature of the system rise continuously. I can't understand why
this problem occur.
Here's is my input script. Any help would be appreciated.

Hi all,
I hope my mail will reach many polymer simulation experts who can guide me
out of my confusion.

This query is regarding the equivalence of reduced density and real density
and the effect of its difference on polymer property like entanglement

I am modeling Polyethylene using full atomistic model rather than coarse
grained one.

Generally, the polymer simulation community working with coarse grained
simulations prefers reduced density values of 0.85 and using same they reach
various entanglement length values of these systems.

For my PE system e.g. if I have the following parameters:
N (No of atoms in simulation box) = 9500, LJ_sigma = 4.28 Angstrom,
Box_length (corresponding to real density of 0.77 grms/cc) = 65.74 Angstrom.

Then, the equivalent reduced density (rho_real) = N * LJ_sigma^3 /
Box_length^3 = 2.62

So, my query is that with this big difference in reduced density, is it
advisable to compare Entanglement length Values of two systems (coarse
grained & full atomistic)?

Other query is: why this magic number 0.85 for reduced density in coarse
grained systems?

In case, my query is bit immature then I will really appreciate if someone
can suggest me some good references!!

Thanks in advance.

Looking forward for enlightenment.

Hi, Ali

I suggest that you examine the units of the variables. In the “fix heat” command, you may give a very large heat flux but with small time interval. I took a rough calculation, the heat flux you give is approximately 1.1E20 w/m^2. It’s not reasonable.

Good luck and good weekend!


在2008-10-11,“Ali Rajabpour” <[email protected]…696…> 写道: