Oscillatory heat current auto correlation function

Dear users,

I am trying to calculate heat current auto-correlation(HCACF) function of Si-nano particles using LAMMPS.
For nano particle of 2 nm diameter HCACF converges after 1ps. This I have seen for temperatures 300,500,700,900 Kelvin.

Even for diameter of 3 nm at 900K HCACF converges but for temperature 300K and 500K HCACF shows oscillatory nature.
Please share your experiences regarding this oscillatory nature of HCACF with the change in particle size if you have any.

Thanks in advance
Amal Giri

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