Please copy to the LAMMPS mailing list, thanks.

Please note that stress/pressure fluctuation can be very large for small systems so that moduli estimated from stresses can vary by a large amount, not to mention its sensitivity to the calculation procedure used. You might want to use the exact same procedure use in your Ref.

Btw, compute stress/atom is an estabilished feature in LAMMPS. I can hardly imagine it being the blame here.

Ray

“Please copy to the lammps mailing list”

Sorry i thought i send it there as well.

Previews reply:

Thanks for the reply Ray,

the thing is that at REF:

Fasolino et al. PRL 102, 046808 (2009)

they performed Monte Carlo calculations and calculated the young modulus to 1TPa with the LcBOP potential (i forgot to mention that to the original post).

Also Fasolino and Los were the ones that developed the LcBOP potential so i guess i should get a young modulus of 1TPa even at 300K.

“Btw, compute stress/atom is an estabilished feature in LAMMPS. I can hardly imagine it being the blame here.”

Yes im sure it works ok, its just that i was worried whether there is any incompatibility with the Partial NPT ensemble i used (since pressure relaxed at one side only).

Anyway thanks a lot.

By the way does anyone know anything about that?

(From the first mail)

"*About the stress per atom formula:*

*http://lammps.sandia.gov/doc/compute_stress_atom.html*

*i noticed it contains kinetic energy terms, pairwise energy terms, plus bond, angles, dihedral, improper and Kspace terms.*

*Since LcBOP is a pair style potential, which of these terms are actually used for the calculation of the pressure? (for example the bond terms should not be used since the pairwise energy should do the same thing.)*"

Which terms of the formula are active during the calculation of the stress tensor?

Thanks,

Aris

"Btw, compute stress/atom is an estabilished feature in LAMMPS. I can

hardly imagine it being the blame here."

Yes im sure it works ok, its just that i was worried whether there is any incompatibility

with the Partial NPT ensemble i used (since pressure relaxed at one side

only).

compute stress/atom does what it should do regardless of the ensemble so

there shouldn't be a problem.

Anyway thanks a lot.

By the way does anyone know anything about that?

(From the first mail)

"*About the stress per atom formula: *

*http://lammps.sandia.gov/doc/compute_stress_atom.html*

<http://lammps.sandia.gov/doc/compute_stress_atom.html>

*i noticed it contains kinetic energy terms, pairwise energy terms, plus

bond, angles, dihedral, improper and Kspace terms.*

Pair_styles do not have contributions from bond, angles, etc, so those

terms are of course zero. For kinetic energy please see the doc page.

Ray