Hi,

I have a question regarding dump custom sxx, syy, etc.

I am making uniaxial elongation of a bulk polyethylene box using

fix/uniaxial. My final strain in z is 0.5.(50 % elongation in z) and I

simulate a system of total 3000 atoms for 10 ns. I dump atomic stress values

(sxx, syy, etc.) and when I check these values, they are very large. To calculate the

normal stress along x at one time step, I add up all the x stress values for

all atoms at that time step (I calculate the other directions in the sam

way) I divide this value by total volume of the box since it's bulk

simulation. But the stress values are too high (on the order of teraPa-way

too high for polyethylene) Also the stress-strain curve does not start at

zero, there's stress even at the first time step. I know the value that

lammps gives includes a kinetic term and the inter-molecular interaction

term but not the intra-terms. I wrote down a code to calculate virial from

the intra-molecular interactions. The values from this code is much smaller

than the LAMMPS contribution. As a result, the overall stress-strain curve

is dominated by lammps results.

I was wondering what I'm doing wrong here. The units of virial is kcal/mol,

right?

Any help is appreciated, thanks so much,

Sezen