problems about Elastic Constants under certian pressure

Dear LAMMPS developers and users,

I want to obatian the elastic constants of cubic silicon carbide under certian pressure. Then I used the ELASTIC example provided in the LAMMPS distribution and changed some commands in the input scripts for adapting to my purpose. Especially, the command “fix 3 all box/relax aniso 0.0” was varied to “fix 3 all box/relax aniso ${press}”, where the variable press is the certian pressure. After tested a couple of different pressure values, I found that the elastic constants were nearly unchanged. However, as shown in some papers the elastic constants change with the pressure of system. Therefore, I consider I must miss some essential seetings. Would someone (especially Aidan) familiar with the elastic constants calculation give me some advice. Any suggestion would be of great help.

Thans & Regards


Well, if the elastic constants are nearly unchanged, it could be that the specified pressure is too small to have an effect. Try making it larger. You can also achieve a similar goal by simply changing the initial lattice constant, removing the fix box/relax command. You will get a non-zero initial pressure that is recorded in the log file.

Dear Aidan, thank you so much.

With your advice I checkd my scripts and found that I had made a mistake that the units used in the simulation was neglected. I would try it again.

Best regards.


2016-03-23 08:14:35,“Aidan Thompson” <[email protected]…24…> :