MOLECULAR-DYNAMICS FREE-ENERGY SIMULATIONS - INFLUENCE OF THE TRUNCATION OF LONG-RANGE NONBONDED ELECTROSTATIC INTERACTIONS ON FREE-ENERGY CALCULATIONS OF POLAR-MOLECULES

The introduction of a reaction held dipolar contribution in free energy calculations is considered. The method is applied to a series of polar compounds, namely TIP3P water, methanol, and acetamide. The hydration free energies computed with both spherical cutoff and reaction field geometries are critically compared. Although the estimated quantities appear to be very similar, the use of a reaction field correction offers a better representation of the liquid structure. In the case of methanol, different potential derived point charge models of increasing complexity are investigated. It is found that the sophisticated models, involving either lone pairs or bond center charges, do not lead to any significant improvement over the simple atomic charge distribution. This trend is correlated to the variable strength of the modeled hydrogen bonds in solution.