Elastic constants of Lennard-Jones fcc crystal

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1

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.

Azat.

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

2

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

Ray

3

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 …
18,20c18,20
< #units metal
< #variable cfac equal 1.0e-4
< #variable cunits string GPa