Hi, I am working on molecular dynamic simulations. I need to find the solubility of a solute (solid) in ionic liquids (solute and solvent are in homogenoius mixturte) by MD simulations. But, I don't know how to find the solubility and activity coefficient of a solute in solvent by MD simulations?. Please help me in calculations. Thanks in advance
Be aware that solubility of a solid in a solution requires two free energies: the standard free energy (chemical potential) in solution compared to the ideal gas, and the free energy in the solid compared to the gas phase. The former can be obtained from simulation, e.g. thermodynamic integration; the latter can best be obtained from simulations in the crystalline state using thermodybnamic integration from an ideal harmonic crystal as intermediate. See the book by Frenkel and Smit ('Understanding simulation') for details.
Widom's particle insertion method does not work in one step for large and complex molecules, but it can be a good starting point: first insert a small molecule by Widom's method, then 'grow' that molecule to full size by T.I. But again: be aware that this yields the solubility from the ideal gas phase, not from the solid.
Hi,
You can get the infinite dilution activity coefficient by computing the excess chemical potential of the solute in the solvent. This can be done by standard procedures such as Widom's test particle insertion.
First calculate the free energy (thermodynamic integration is a good method). With free energy you can get the activity coefficient
Be aware that solubility of a solid in a solution requires two free energies: the standard free energy (chemical potential) in solution compared to the ideal gas, and the free energy in the solid compared to the gas phase. The former can be obtained from simulation, e.g. thermodynamic integration; the latter can best be obtained from simulations in the crystalline state using thermodybnamic integration from an ideal harmonic crystal as intermediate. See the book by Frenkel and Smit ('Understanding simulation') for details.
Widom's particle insertion method does not work in one step for large and complex molecules, but it can be a good starting point: first insert a small molecule by Widom's method, then 'grow' that molecule to full size by T.I. But again: be aware that this yields the solubility from the ideal gas phase, not from the solid.
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