Elastic Modulus calculation for RDX using rxff based on example elastic modulus script

Please reply to the list.

I can obtain elastic constants for RDX in the reasonable range without a problem. Check my second comment below again. You are also equilibrating for a long duration of time – that might have had an effect.


So can I have a look at your lmp_control file and also why would equilibrating for a long time have an effect on the results.

Can you please discuss your schedule and the range of values for C11, C22 and C33 which you are getting.

Did you check the results with my scripts, with some modifications. And what is the number of atoms in your system?

I used “NULL” as implied in my previous reply.

I used 1% strain and a 168-atom supercell. All constants reasonable.

Sorry I don’t have to time to run your script and check your results.


Dear Lammps Users,

I tried with the schedule Ray mentioned and tried it original reaxFF as well as its LG variant, but still could not get all 3 values reasonable. Only C11 is somewhat reasonable.

So if you do not mind can I have a look at scripts and see what mistakes I am doing, as I have now tried with different size including the one Ray suggested and different strain rates and different reax force fields but still I am off in 2 values.

Please help and advise.

Did you try “NULL” instead of using a control file?


Yeah I tried that with a unit cell of 168 atoms and I was still off. But I tried it with a lower strain rate of 0.1% and it seems reasonable now for LG variant of rxff but not for the no LG version.

So I just want to know how to ensure proper values because now I have tried systems with different number of atoms with an without control file and different strain rated and all of them are not reasonable.

So I am doing something wrong but not sure what that is.

One easy question for you: in your script you used a structure named “data.rdx”. Where did you get this structure?