Hello everyone,

I am using LAMMPS with LJ units and have calculated diffusion. I am aware that LJ units are unitless, but I am wondering how I can convert my diffusion results to real substances.

I read the LAMMPS and Units documentation but struggled to convert the model to SI units. I couldn’t find a clear example to follow.

For instance, I would like to transfer a model that calculates the diffusion of CO2 in SI units.

the following model is from “Yu Zhu”, “Prediction of diffusion coefficients for gas, liquid, and supercritical fluid: application to pure real fluids and infinite dilute binary solutions based on the simulation of Lennard–Jones fluid”

Eq:

D^*_{LJ}=\frac{3}{8\sqrt{\pi}}\frac{\sqrt{T^*}}{n^*}\times\Big(1-\frac{n^*}{a(T^*)^b}\Big)\Big[1+(n^*)^c\Big(\frac{d(n^*-1)}{e(n^*-1)+(T^*)^{f+gn^*}}+h\Big)\Big]\times\exp\Big(-\frac{n^*}{2T^*}\Big)

He calculated for CO2, but I was wondering how can we do that?