# How to calculate the elastic modulus of bulk materials composed of LJ particles

Dear all users:
I am very interested in the elastic modulus of bulk materials composed of LJ particles, what i should do is as follows:build the fcc bulk structure composed of LJ particles, and input the LJ pair potential into lammps script, then do the uniaxial tension and get the stress-strain curve,calculate the elastic modulus at last. Am I right? Does any three-body potential effect or many-body potential effect will affect the result greatly? As I know,we use EAM potential to calculate the elastic modulus of metal crystal, and the EAM potential concludes many-body effect, and only using pair potential of metal atoms can not describe the metal crystal properly.we know LJ potential is a classical pair potential, if we know a kind of bulk materials composed of particles, and the pair potential between particles is already known, can we calculate the elastic modulus of it just like the way of bulk materials composed of LJ particles? Thank you very much!
best wishes
Xuepeng Liu

Dear all users:
I am very interested in the elastic modulus of bulk materials composed of LJ
particles, what i should do is as follows:build the fcc bulk structure
composed of LJ particles, and input the LJ pair potential into lammps
script, then do the uniaxial tension and get the stress-strain
curve,calculate the elastic modulus at last. Am I right? Does any three-body
potential effect or many-body potential effect will affect the result
greatly? As I know,we use EAM potential to calculate the elastic modulus of
metal crystal, and the EAM potential concludes many-body effect, and only
using pair potential of metal atoms can not describe the metal crystal
properly.we know LJ potential is a classical pair potential, if we know a
kind of bulk materials composed of particles, and the pair potential between
particles is already known, can we calculate the elastic modulus of it just
like the way of bulk materials composed of LJ particles? Thank you very
much!

you are mixing up two different things:
- does computing the elastic modulus require a specific type of potential?
- does the lennard-jones potential represent materials well?

the answer to the first question is: no.
the answer to the second question is: it depends on the material. LJ
is popular, because it is simple, computationally very efficient and
for materials that have gas-like interactions, it is often a
reasonable approximation. but then again, it cannot be as accurate as
a quantum monte carlo calculation, for example. but the latter is much
more costly. so it all depends on what level of accuracy you need,
what level of transferability you need and what amount of
computational effort you can afford.

axel.

Dear axel:
Thank you very much for your advice! I know LJ pair potential is simple and reasonable,and most important it is computationally efficient. now I seek the inexpensive computation of simulation. for the system is complicated, and the bulk materials is made of identical particles,but the pair potential between two particles is already known(assume it is correct), Can we treat the particles as atoms, and input the pair potential into lammps, and build the fcc or bcc or any other 3d structure to calculate the elastic modulus of bulk material? or we should modify the pair potential which consider the many body effect then input into lammps?thanks very much!
best wishes
Xuepeng Liu

Dear axel:
Thank you very much for your advice! I know LJ pair potential is simple and
reasonable,and most important it is computationally efficient. now I seek
the inexpensive computation of simulation. for the system is complicated,
and the bulk materials is made of identical particles,but the pair potential
between two particles is already known(assume it is correct), Can we treat
the particles as atoms, and input the pair potential into lammps, and build
the fcc or bcc or any other 3d structure to calculate the elastic modulus of
bulk material? or we should modify the pair potential which consider the
many body effect then input into lammps?thanks very much!

since you are repeating the same question, i have to repeat the same answer.

axel.

Dear axel: