Dear Sheida

I'm not the right person you expected to answer your question (Jobic) but i suggest you to repeat the md simulations using force field parameters you can extract in high level of ab initio calculations (regarding to small molecular size of ammonia).

Be happy

In addition to the above comments, note that diffusion coefficients in periodic systems need to be corrected for size effects.

http://pubs.acs.org/doi/abs/10.1021/jp0477147

Have you tried a simulation of the pure fluid as a first step? Ludemann has measured the self-diffusion coefficients over a wide range of thermodynamic states.

Gross, T; Buchhauser, J; Price, WE; et al. The p,T-dependence of self-diffusion in fluid ammonia JOURNAL OF MOLECULAR LIQUIDS 1997, 73-4, 433-444

See also

Hardy, EH; Zygar, A; Zeidler, MD; et al. Isotope effect on the translational and rotational motion in liquid water and ammonia

JOURNAL OF CHEMICAL PHYSICS 2001, 114 , 3174-3181

Dear All,

Special thanks for the cmnts.

Seyyed Jalil,

Indeed, I am not familiar with ab inition calculations; however, tnx for ur cmnt. I'll try to check it.

Abel,

I performed NVT simulation for a system containig almost 2350 atoms. unfortunatally, there is lack of references in my studied field. I examined self diffusion of NO, NH3, N2, N2O, and NO2. I've already found an article which report MD results for N2 diffusion. The obtained results were similar to mine and in the same order of magnitude. I am wondering if I could rely to the mentioned paper for confirming my other simulations...

Best to All,

Sheida

Dear Justin & Kenneth

Tnx for your offers.

Will check the references.

Best,