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 energ y calculations is considered. The method is applied to a series of pol ar compounds, namely TIP3P water, methanol, and acetamide. The hydrati on free energies computed with both spherical cutoff and reaction fiel d geometries are critically compared. Although the estimated quantitie s appear to be very similar, the use of a reaction field correction of fers a better representation of the liquid structure. In the case of m ethanol, different potential derived point charge models of increasing complexity are investigated. It is found that the sophisticated model s, 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 hyd rogen bonds in solution.