where G is the Gibbs free energy, and N i is the number of molecules of i in solution; P, T , and N H 2 O are the pressure, absolute temperature, and number of water molecules in solution, and are kept constant in the calculation. One important aspect to discuss is reason why we chose to calculate the Helmholtz free energy for the solid and Gibbs free energies for each solution. Solid state simulations with position restraints required running under constant temperature and constant volume conditions due to software limitations, therefore we were able to calculate A for the solids.. At constant pressure, both kinds of free energy are related by: