I am using the following code to compute the components needed to calculate the stress relaxation modulus G(t) according to Eq. 4 in Ref:

```
compute c_stressA all stress/atom
compute pA1 all reduce sum c_stressA[1]
compute pA2 all reduce sum c_stressA[2]
compute pA3 all reduce sum c_stressA[3]
compute pA4 all reduce sum c_stressA[4]
compute pA5 all reduce sum c_stressA[5]
compute pA6 all reduce sum c_stressA[6]
variable nxy equal c_pA1-c_pA2
variable nxz equal c_pA1-c_pA3
variable nyz equal c_pA2-c_pA3
fix 5 all ave/correlate/long 1 1000 c_pA1 c_pA2 c_pA3 c_pA4 c_pA5 c_pA6 v_nxy v_nxz v_nyz type auto nlen 16 ncount 2 ncorr 30 file output-folder/output-file.out.correlate.txt
```

Naïvely, I would expect the output to have rows, one row for each time-step at which to output, containing the auto-correlated values of all the variables & computes I pass.

However, the output of the fix ave/correlate/long contains sections, one for each time-step at which LAMMPS outputs, each section with an additional column “Time”.

My question is, what does this “Time” column represent, where does it come from, which “Time” do I want to use to plot G(t) vs t?

This is a question I should in theory be able to answer by reading the code of LAMMPS, which I am currently doing, but it seems to be more involved than I might have hoped. I would update this post if/when I do find an answer.