Choice of the center of water molecules in calculations of partial molar volume of single ions immersed in water: A molecular simulation study

In the Kirkwood-Buff theory, the center of each solvent molecule can be arbitrarily chosen. However, this arbitrariness is not obvious in the calculation of the Kirkwood-Buff integral for a single ion. Actually, the Kirkwood-Buff integral depends on the choice of the center of a solvent molecule, if each solvent molecule has a dipole moment and the solute has a net charge. A few examples based on molecular dynamics simulations are shown. A surrogate definition for the center of a water molecule is also shown. A good agreement between the calculated and experimental values of partial molar volumes for single ions is observed.