MOLECULAR-DYNAMICS SIMULATION OF THE ENERGY-DISTRIBUTIONS OF MOLECULES IN LIQUID SOLUTIONS

A solution is modelled as a classical 2D molecular system consisting o f two types of molecules having different interaction parameters. The interaction is modelled by Lennard-Jones -type potentials. Molecular D ynamics simulations of solutions of soft molecules imbedded into a bat h of rather hard solvent molecules are performed. From the molecular d ynamics trajectories we derive the energy distributions and study loca l energy excitations of the solute and the solvent molecules. In parti cular the dynamics of activation processes (high energy events) is inv estigated for a special model: We simulate the thermal equilibrium of one molecule with Lennard-Jones 8-6-interactions imbedded into a bath of molecules with 18-6 interactions. It is shown that in thermal equil ibrium a region of temperatures and densities exists, where the mean o ne-particle energy has a relative maximum. In this region the potentia l part of the thermal energy is preferably partitioned to the solvent molecules. Further we show that the energy distribution of the soft mo lecules shows longer rails than that of the hard molecules. On the bas is of these distributions it is concluded that energy spots at the sol ute molecules may appear which possibly could lead to the enhancement of solute reactions.(1).