Hi

In two below formulas:

and

about N,

I simulate the diffusivity of O2 in Polyethylene.

Cell: 30 O2 + 4 PE chains.

The calculated D, according to the slope of MSD vs t, (around 5.4 * 10^-6) is higher than the experimental D (around 1.7 * 10^-7).

But, when i divide the 5.4 * 10^-6 by 30 (number of O2 molecules), it is 1.8* 10^-7 that is close to the experimental D.

Is it correct or not?