CNT Youngs Modulus

Dear all

I did MD simulation for CNT using LAMMPS in order to compute Young’s Modulus. when atomic atom style and REBO inter-atomic potential were chosen, the results were reliable and compliance to literature.I decide to chose another inter-atomic potential so I find an article and find proper potential. The potential consist of pairwise , bond , angle , dihedral , improper . so I define each of them separately.

pair_style lj/cut 10
pair_coeff * * .006 3.617

bond_style harmonic
bond_coeff 1 20.814432 1.34

angle_style harmonic
angle_coeff 1 3.902706 120

dihedral_style harmonic
dihedral_coeff 1 0.1300902 -1 2

improper_style cvff
improper_coeff 1 0.016044458 -1 2

in order to define and load atom position I had to chose molecular atom style. after running inputs file the result was disappointing. the stress increase gradually up to 900 GPa and CNT didn’t break,
what is my fault?I will be glad if any could give me best advice.

Dear all

I did MD simulation for CNT using LAMMPS in order to compute Young's
Modulus. when atomic atom style and REBO inter-atomic potential were chosen,
the results were reliable and compliance to literature.I decide to chose
another inter-atomic potential so I find an article and find proper
potential. The potential consist of pairwise , bond , angle , dihedral ,
improper . so I define each of them separately.

[...]

in order to define and load atom position I had to chose molecular atom
style. after running inputs file the result was disappointing. the stress
increase gradually up to 900 GPa and CNT didn't break,
what is my fault?

yes, in a way it is your fault. bond defined with a harmonic
potential *cannot* break. that is the very nature of the
functional form. also, to expect that such a simple (and
computationally cheap) potential would be competitive
with a so much more sophisticated model as REBO is
ignoring the realities of classical force fields.
something's gotta give, if you use a simpler model.

axel.