correlation calculation of per atom Stress

Dear Lammps Users,

I would like to ask for the advise for calculation of per atom correlation of stress over time and average it over all atoms at the end.

I tried some compute and also Fix ave/corrolate and fix ave/corrolate/long commands but it seems they only calculate the correlation for bulk value of variable (mine would be stress). More clearly I am interested in calculation of relaxation modulus G(t).

Should I change the code for that or there is some other way to do so? Y’all know It is not feasible to store all snapshot and post-process it.

I appreciate any comment and advise or even weblink in this matter.

Best

Matt B

UT

Dear Lammps Users,

It my second time writing my question.

I would like to ask for the advise for calculation of per atom correlation of stress over time and average it over all atoms at the end.

I tried some compute and also Fix ave/corrolate and fix ave/corrolate/long commands but it seems they only calculate the correlation for bulk value of variable (mine would be stress). More clearly I am interested in calculation of relaxation modulus G(t).

Should I change the code for that or there is some other way to do so? Y’all know It is not feasible to store all snapshot and post-process it.

I appreciate any comment and advise or even weblink in this matter.

Best

MB

UTK

You can see the compute heat/flux command for
example code that used fix ave/correlate with stress as an input.

Not sure what you mean by correlation of a bulk value versus
something else.

Steve

Dear Steve,

Thank you for your email.

For my purpose I want to calculate correlation of per atom stress values over time, and then calculate the ensemble average for each timestep. Fix ave/correlate do not calculate the correlation of vectors, I was asking if there is a command to do so.

I tried to extract the stress of specific atoms and use fix ave/correlate, but I didn’t succeed. I may need to make some changes to Fix ave/correlate to see if it can calculate the correlation of the vector of atom stress [{1}:{number of atoms}].

Thanks

MB

You are right, there is no command in LAMMPS to correlate per-atom vectors.

Steve