In our previous work

we endowed a new physical meaning of self-diffusion coefficient in Fick's law

which proposed that the diffusion coefficient can be described as the product of the characteristic length and the diffusion velocity. To testify this simple theory

in this work

we further investigated the underlying mechanism of the characteristic length and the diffusion velocity at the molecular level. After a complete dynamic run

the statistical average diffusion velocity and the characteristic length of molecules can be obtained by scripts

and subsequently the diffusion coefficient was determined by our proposed theory. The diffusion processes in 35 systems with a wide range of pressure and concentration variations were simulated using this model. From the simulated results

diffusion coefficients from our new model matched well with the experimental results from literatures. The total average relative deviation of predicted values with respect to the experimental results is 8.18%

indicating that the novel model is objective and rational. Compared with the traditional MSD-

t

model

this novel diffusion coefficient model provides more reliable results

and the theory is simple and straightforward in concept. Additionally

the effect of gas pressure and liquid concentration on the diffusion behavior were discussed

and the microscopic diffusion mechanism was elucidated through the distribution of diffusion velocity and the characteristic length analysis. Moreover

we suggested new distribution functions

providing more reliable data theoretical foundations for the future research about the diffusion coefficient.