Hi Axel,

Both of the two curves represent the normal stress along tensile direction. The black line is that I used the “compute pressure” command to calculate the normal stress(pzz), while the red line I used the command “compute stress/atom” and use the “compute reduce” to calculate the normal stress(sigmazz), I think they are should be the same, but the result does not. I use these two method in the other materials, they are the same. So which method is better to calculate the normal stress during the tensile test.

Best wishes!

Compute pressure use the box dimension to calculate the pressure.

Compute stress/atom does not calculate any pressure, but

pressure*volume. Because you don't mention the use of Voronoi volume, I

assume you use here the volume of the box to get the value in pressure

unit. It seems to me relatively ill-defined to use the box volume with

stress/atom without a box fully periodic...

Hi Axel,

Both of the two curves represent the normal stress along tensile direction.

in what units?

The black line is that I used the "compute pressure" command to calculate

the normal stress(pzz), while the red line I used the command "compute

stress/atom" and use the "compute reduce" to calculate the normal

stress(sigmazz), I think they are should be the same, but the result does

not. I use these two method in the other materials, they are the same. So

which method is better to calculate the normal stress during the tensile

test.

impossible to say. both should give *identical* output, if computed

correctly. since you don't provide enough information to assess how you

computed them, there is no way to tell. they could be both wrong.

axel.

Compute pressure use the box dimension to calculate the pressure.

Compute stress/atom does not calculate any pressure, but pressure*volume.

Because you don't mention the use of Voronoi volume, I assume you use here

the volume of the box to get the value in pressure unit. It seems to me

relatively ill-defined to use the box volume with stress/atom without a box

fully periodic...

compute pressure does the same thing. ...and the sum of all voronoi

volumes is the box volume, so for as long as this is computing the sum over

all per atom stresses, this should be comparable. in fact, the compute

stress/atom docs give an example for how to compute the same result as what

compute pressure gives.

axel.

Thanks for the precision Axel! I wasn’t indeed sure whether the the Voronoi cell would be limited by the simulation box or the paire_style cutoff, in the particular case when the paire_style cutoff extends “outside” a non-periodic boundary. Julien