Elastic constants of Lennard-Jones fcc crystal

Hello, dear LAMMPS developers!

I tried to calculate elastic constants of Lennard-Jones fcc crystal at zero temperature by using scripts in /examples/ELASTIC.

Block box containing 32000 LJ particles has been created and units lj was changed into init.mod , but I am confused with cfac and cunits values.
Also pair_style, pair_coeff, neighbor, and neigh_modify command in potential.mod were changed.

Can you give me any advise?,
because keeping original values, LAMMPS stops running at xy deformation, saying
ERROR: Cannot change box tilt factors for orthogonal box (…/change_box.cpp:252)

I think the solution of this problem will be helpful for all LAMMPS users, studing LJ model due to its prevalence.

I appreciate any help.


p.s. There was no problem with running the original scripts from /examples/ELASTIC on my PC.

You need to add a change box command to change the box from orthogonal
to triclinic.


If you make these changes to init.mod and potential.mod, you will get the elastic constants for the LJ FCC lattice with nearest neighbor interactions, which are:

C11 = 72.00000000000000000000000000
C12 = C44 = 36.00000000000000000000000000000

[athomps@…2929… LJ_FCC]$ diff init.mod …
< #units metal
< #variable cfac equal 1.0e-4
< #variable cunits string GPa