We find an interesting interplay between the range of the attractive part of the interaction potential and the extent of metastability (as measured by supersaturation) in gas-liquid nucleation. We explore and exploit this interplay to obtain new insight into nucleation phenomena. Just like its dependence on supersaturation (S), the free energy barrier of nucleation is found to depend strongly on the range of the interaction potential. Actually, the entire free energy surface, F(n), where n is the size of the liquid-like cluster, shows this dependence. The evidences and the reasons for this strong dependence are as follows. (i) The surface tension increases dramatically on increasing the range of interaction potential. In three dimensional Lennard-Jones system, the value of the surface tension increases from 0.494 for a cut-off of 2.5 {sigma} to 1.09 when the full range of the potential is involved. In two dimensional LJ system, the value of the line tension increases from 0.05 to 0.18, under the same variation of the potential range. (ii) The density of the gas phase at coexistence decreases while that of the liquid phase increases substantially on increasing the range of the interaction potential. (iii) As a result of the above, at a given supersaturation S, the size of the critical nucleus and the free energy barrier both increase with increase in the range of interaction potential. (iv) Surprisingly, however, we find that the functional form predicted by the classical nucleation theory (CNT) for the dependence of the free energy barrier on the size of the nucleus to remain valid except at the largest value of S studied. (v) The agreement between CNT prediction and simulated values of the barrier is supersaturation dependent and worsens with increase in the range of interaction potential, and increases above 10 kBT at the largest supersaturation that could be studied.
Download